Joe Nieberding and Craig H. Williams

Glenn Research Center, Cleveland, Ohio

ADDJUST—A View of the First 25 Years

NASA/TM—2015-218752

May 2015

AIAA–2014–3672
NASA STI Program . . . in Profile

Since its founding, NASA has been dedicated 

to the advancement of aeronautics and space science. 

The NASA Scientific and Technical Information (STI) 

Program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Officer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI Program provides access 

to the NASA Technical Report Server—Registered 

(NTRS Reg) and NASA Technical Report Server—

Public (NTRS) thus providing one of the largest 

collections of aeronautical and space science STI in 

the world. Results are published in both non-NASA 

channels and by NASA in the NASA STI Report 

Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major significant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of significant 

scientific and technical data and information 

deemed to be of continuing reference value. 

NASA counter-part of peer-reviewed formal 

professional papers, but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientific 

and technical findings that are preliminary or of 

specialized interest, e.g., “quick-release” reports, 

working papers, and bibliographies that contain 

minimal annotation. Does not contain extensive 

analysis.

• CONTRACTOR REPORT. Scientific and 

technical findings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientific and technical 

conferences, symposia, seminars, or other 

meetings sponsored or co-sponsored by NASA.

• SPECIAL PUBLICATION. Scientific, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific and 

technical material pertinent to NASA’s mission.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question to help@sti.nasa.gov

• Fax your question to the NASA STI 

Information Desk at 757-864-6500

• Telephone the NASA STI Information Desk at

757-864-9658

• Write to:

NASA STI Program

Mail Stop 148

NASA Langley Research Center

Hampton, VA 23681-2199
Joe Nieberding and Craig H. Williams

Glenn Research Center, Cleveland, Ohio

ADDJUST—A View of the First 25 Years

NASA/TM—2015-218752

May 2015

AIAA–2014–3672

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

50th Joint Propulsion Conference

cosponsored by the AIAA, ASME, SAE, and ASEE

Cleveland, Ohio, July 28–30, 2014
Acknowledgments

The authors would like to thank and acknowledge the extraordinary contributions of Mr. Daniel Swanson and his exemplary team 

at General Dynamics, and of Mr. Jack Estes of NASA Lewis. Without Dan’s expertise in trajectory design and Jack’s experience 

in wind data interpretation and loads calculations, I seriously doubt that ADDJUST could have been developed.

Available from

Level of Review: This material has been technically reviewed by technical management. 

NASA STI Program

Mail Stop 148

NASA Langley Research Center

Hampton, VA 23681-2199

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

703-605-6000

This report is available in electronic form at http://www.sti.nasa.gov/ and http://ntrs.nasa.gov/
ADDJUST—A View of the First 25 Years

Joe Nieberding* and Craig H. Williams

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

Various technologies and innovative launch operations were

developed during the 50 years of the Centaur upper stage—the 

first launch vehicle to use high performing liquid hydrogen fuel. 

One innovation was “ADDJUST”, which enabled the successful negotiation of upper level winds measured only hours before 

launch. Initial causes for its creation, development, and operation during countdown are detailed. Problem definition, wind 

measuring/monitoring process, pitch and yaw steering coefficient generation, loads analysis, angle of attack, major 

risks/concerns, and anecdotal recollections are provided. 

Launch availability improved from as low as 55 to 95 percent

due to ADDJUST, which is still in use. 

Nomenclature

P pitch

Y yaw

h height

Δ change

θ steering angle

1.0 Introduction

This paper recounts my personal experiences with the history 

of Atlas/Centaur’s progression of techniques over the years to 

deal with safe flight through the upper level winds. As a retired 

NASA engineer after 35 years on the Centaur project at NASA 

Lewis (later renamed Glenn), I share my recollections on the 

problems we had and the solutions we adopted. In many cases, 

original charts were used for historical authenticity when they 

were available. ADDJUST is the acronym for Automatic Determination and Dissemination of Just Updated Steering 

Terms. The acronym is attributed to Mr. Frank Anthony of 

General Dynamics, Convair division, which manufactured the 

Atlas and Centaur stages for Lewis in San Diego. ADDJUST is

the automated computer and communication system used to 

provide Atlas/Centaur and, later, Titan IIIE/Centaur, with open 

loop, booster phase steering data on launch day. It still flies 

*

 Retired

today on Centaur as the upper stage for Atlas V. The first paper

published on ADDJUST was written by Daniel C. Swanson of 

General Dynamics, Convair Division, in 1976 (Ref. 1). While

Swanson expertly recounted the technical aspects of ADDJUST

in that brief paper (also presented in some detail here), this paper also provides a historical view of ADDJUST, with perspectives unique to NASA. Reference 1 described ADDJUST 

results only up to the mid-1970s time frame, where this paper 

discusses results through 1998. Some materials are originally

from an unpublished presentation co-authored by the first author (Ref. 2) No attempt was made to discuss the modern United 

Launch Alliance (ULA) implementation of ADDJUST on the 

current Atlas V launch vehicle. 

The Centaur upper stage was first flown successfully in 1963. 

The launch of an early Atlas/Centaur (AC) configuration is 

shown in Figure 1. Centaur was initially developed as an upper 

stage for the Atlas booster to fly the Surveyor lunar soft lander 

missions beginning in 1966. It later flew on Titan IIIE/Centaur 

as well. Centaur is best known for becoming the first upper 

stage to use liquid hydrogen as a fuel. But it also pioneered the 

development of other technologies, including an innovative approach to successfully negotiate upper level winds. That approach was called ADDJUST. This paper addresses my 

recollections of its development, how it worked, why it was so 

critically needed, and its performance through the late 1990s. In 

1998 the Centaur program was transferred from Lewis to Kennedy Space Center, Florida. Major risks and mitigations are discussed. 

NASA Lewis Research Center directed General Dynamics 

(GD), to develop the ADDJUST system for Atlas/Centaur in 

1972, following a series of costly launch aborts due to upper 

level flight wind restrictions. Requirements for ADDJUST development were to automate existing computer programs on 

GD’s scientific computer in San Diego, to interface the system 

with existing flight wind restriction procedures, to communicate results to Lewis for independent verification and validation 

(IV&V) and to the launch complexes, with minimum impact 

on launch operations. ADDJUST was to provide for rapid 

design, trajectory/performance validation, and transfer of 

wind-biased pitch and yaw steering terms. It was required to 

NASA/TM—2015-218752 1 

 
respond to data from balloon soundings released from the Eastern Test Range (ETR) about 2.5 hr before liftoff. The Atlas/Centaur target launch availability (statistical probability of 

launching through the flight winds, see Sec. 4.1) was set at 

90 percent for the worst winter months, compared to the existing 55 percent with techniques then in use. The decision to 

launch Centaur would be made only after all Mission Acceptance Criteria (see Sec. 4.4) were met, based on prelaunch 

GD calculations independently verified by Lewis.

2.0 Background

A typical flight profile for Atlas/Centaur is shown in Figure 2

(Ref. 3) Atlas and Titan boosters accelerated the Centaur upper 

stage through the atmosphere. Steering commands during the 

booster phase were computed by Centaur, using constants that 

were remotely loaded during the prelaunch countdown. Flight 

guidance was broken up into an open loop booster phase and a 

closed loop, exoatmospheric phase. The ADDJUST system provided the wind-biased steering data used only in the open loop 

phase of booster flight. Most loads that will occur in flight can 

be calculated well in advance of the launch date (see Sec. 4.5). 

One effect, however, that of prevailing, variable, upper level atmospheric wind conditions, must be accounted for just prior to 

launch in order to maximize the probability of launching 

through these winds. The wind loads were reduced in flight by 

using biased booster phase pitch and yaw steering programs that 

compensated for winds aloft by reducing the vehicle’s angle of 

attack in the critical regimes where high dynamic pressures 

were encountered. Prior to ADDJUST, a set of pitch and yaw 

programs based on synthetic or seasonal mean winds was provided and stored in a preprogrammed “library” in the Centaur 

ground computer at Launch Complex 36. A rapid search procedure was employed to select the best combination of these pitch 

and yaw programs to minimize the wind loads and meet all the 

Mission Acceptance Criteria. This combination of prestored 

programs was then loaded into the Centaur flight computer. The 

entire library of programs had been verified many weeks before 

launch.

But starting with AC-30 in 1973, after the Centaur had experienced a series of costly launch scrubs because of unacceptably 

high predicted flight wind loads, it was decided that pitch and 

yaw steering programs had to be specifically designed and tailored to the launch day measured wind. These steering programs would then be uploaded to the Centaur computer shortly 

before launch. The tasks of designing these programs, verifying 

that the loads and all other critical Mission Acceptance 

Criteria were met, and reliably transmitting the programs from 

San Diego to the vehicle ground computer on the pad in Florida 

were under control of a computer program called ADDJUST. 

Typically, these programs were then uploaded into the Centaur 

flight computer within about 20 min of launch (sometimes 

much less). These rapid transmissions were made possible by 

the development of computer remote terminal equipment with 

supporting hardware and software which allowed large scale, 

home based scientific computers to be used in near real time 

applications. These capabilities allowed multi-stage design, 

analysis, validation and error free communications programs 

required for ADDJUST to be linked together and controlled by 

remote terminals. Inputs to and outputs from a computer were 

exchanged with remote site computers using ordinary, voice 

band telephone circuits. The predicted results provided the basis 

for a GO/NO-GO recommendation.

Figure 1.—Early Atlas/Centaur Launch

NASA/TM—2015-218752 2 
Figure 2.—Typical Flight Profile of Atlas/Centaur

3.0 Brief History

In the early to mid-1960s, Centaur used four preprogrammed 

pitch profiles, one for each season. Each profile was a set of open 

loop pitch rate versus time commands. Initially, we flew nine

launches without scrubbing for winds, i.e., one of those programs 

resulted in acceptable mission criteria, notably structural loading. 

(Even in the early 1970s, scrubs cost about 1 million dollars per 

day). Over time, since Centaur was always under pressure to increase its payload capability, we lengthened the Atlas tank and 

increased the booster thrust, so we became more susceptible to 

wind loads. Eventually we evolved to a 10 x 10 matrix of programs, now both pitch and yaw, to minimize weather-related 

scrubs. These expanded choices worked quite well into the early 

1970s, until we scrubbed the launch of AC-25 in 1971, for our 

first commercial customer, Intelsat. We then expanded the matrix 

again, this time to include 10,000 pitch and yaw combinations, 

first used on AC-27 in 1972, the first launch of a Pioneer

spacecraft to Jupiter. With so many choices, we felt that we could 

surely find a combination that would work. Table 1 contains a 

summary of the evolution of the booster steering programs. 

As I recall we only had a dozen or so possible launch days

for AC-27 and we scrubbed for winds the first three of them, 

causing significant concern. We successfully launched on the 

fourth day, to the great relief of all. But for the first three days, 

we had not been able to find a combination that worked, as we 

then realized that the problem was that we just couldn’t search 

through 10,000 combinations in a timely fashion. After AC-27 

launched, our Center Director, Mr. Bruce Lundin, came up to 

me in a restaurant in Cocoa Beach, Florida, and asked when our 

next planetary launch would be. I explained that it would occur 

in 13 months, AC-30 to Jupiter, and he said “You’ve got 13 

months to find a better way to fly through the winds.” Clearly, 

we had precious little time to find some other, drastically different, approach.

NASA/TM—2015-218752 3 
TABLE 1.—BOOSTER STEERING PROGRAM EVOLUTION

Dates No. of 

vehicles 

Centaur 

Booster 

Type of 

Booster Steering

1962 to 1966 9 Atlas Seasonal pitch programs (4)

1967 to 1972 18 Atlas Predesigned launch day-selectable pitch and yaw programs (10 pitch and 10 yaw)

1972a 1 Atlas Predesigned launch day-selectable pitch and yaw programs (10,000 pitch and 

yaw combinations)

1973 to 2006 >100 Atlas Launch-day-designed pitch 

and yaw programs 

8 Titan (ADDJUST) 

a Scrubbed 3 days for winds!!

4.0 ADDJUST Development

Immediately after the AC-27 launch, Lewis management 

asked Mr. Jack Estes and me to co-lead the ADDJUST activity 

for Lewis. We went to out to GD, in San Diego, who then appointed about a six person team headed by Mr. Daniel Swanson, 

who authored the initial, brief paper on ADDJUST (Ref. 1). It 

was clear that the new approach had to design a pitch program 

and yaw program tailored to the wind measured on launch day, 

as opposed to searching for a preprogrammed combination designed for some simplified, synthetic wind profile. The first 

breakthrough idea was that, unlike former programs which were 

pitch and yaw rate versus time, we needed to design the new program as attitude versus altitude. The wind profile is measured as 

speed and direction versus altitude, not time of flight. This approach eliminated variations resulting from booster thrust dispersions, i.e., it eliminated uncertainties in the time the vehicle 

achieved a particular altitude. If no wind were simulated, a trajectory design produced a vehicle attitude history (or profile) resulting in zero angle of attack. To achieve zero angle of attack 

when non-zero winds were considered, the resulting attitude history for zero angle of attack varied slightly, or be “biased” from 

the zero wind attitude profile. Much of the following technical 

data in this section was resident (or implicit) in the “Countdown 

Summary, Launch/Hold Criteria, and Flight Events” document 

GD prepared each launch (Ref. 4).

4.1 Wind Filtering

First we needed to measure the wind profile, and then resolve 

it into pitch and yaw component profiles, depending on the 

launch azimuth (Figure 3). Then we had to apply some kind of 

filter to the pitch and yaw profiles separately. The wind had to 

be smoothed, or filtered, to avoid designing or “tuning” to exactly the real measured wind because the high frequency

Figure 3.—Pitch and Yaw Components

of Wind Velocity Vector.

wind characteristics would no longer be present by the time the 

vehicle ascended to the critical altitudes (typically 30,000 to 

50,000 ft, and about 2 hr after the measurement was taken by 

balloons. See Sec. 4.6). If the filter smoothed the wind too 

much, however, it would approach the case of the ill-tuned synthetic winds which were incapable of producing acceptable

launch availability. Finding the proper amount of smoothing 

was critical. We would then design the trajectory profiles to the 

filtered, or smoothed, wind. Later, of course, we had to fly the 

resulting ADDJUST pitch and yaw profile through the real 

wind to verify all mission critical parameters.

After considerable trial and error and judgment by team 

members experienced in analyzing wind profiles, we employed 

a running average technique which eliminated high frequency 

wind components in the creation of a “filtered,” or “design,” 

wind. For the vertical rise phase, 0 to 1,200 ft, there was no 

filtering. From 1,200 to 8,000 ft, the trajectory was designed for 

overall trajectory shaping, i.e., this interval shaped the trajectory to meet the mission orbital requirements, e.g. earth orbital, 

lunar, planetary, etc. The ADDJUST “biasing” of the required 

attitude history was just a small dither or “adjustment” (or is it 

ADDJUSTMENT?) which could be applied to any overall mission shaping. It was critical that the overall mission trajectory 

shape be calculated first, and then ADDJUST applied to reduce 

the angle of attack. The pitch profile was designed to achieve 

the proper integrated heating (mission dependent) at booster engine cutoff (BECO), and the velocity heading in yaw was designed to be the same as if no yaw were performed. This was 

accomplished by a simple 2X2 iteration, i.e., iterate on initial 

pitch attitude at the beginning of this altitude segment to hit the 

right integrated heating, and on the initial yaw attitude to yield 

the proper yaw heading at BECO. This iteration with two control variables and two end conditions had to be kept simple to 

NASA/TM—2015-218752 4 
ensure convergence on launch day (see Figure 4 and Figure 5). 

We were always concerned about whether ADDJUST would 

converge—but it always did.

Since there were no wind concerns in this interval (slow 

speed, low dynamic pressure), there was no wind filtering, and 

the trajectory was not yet designed for zero angle of attack. The 

third phase was designed to minimize pitch and yaw angles of 

attack and resultant air loads through booster engine cutoff 

(BECO). In this phase, between 8,000 and 16,000 ft, we represented the filtered wind by linear segments between averaged 

values at 8,000, 12,000, and 16,000 ft. The raw wind data was 

measured at 200 ft intervals. Any residual angle of attack at 

8,000 ft was forced to decay to zero over the next 10 sec to ensure smooth vehicle responses. At every 200 ft altitude increment above 16,000 ft, we averaged the wind speed data over an 

interval of 6,000 ft. Measured wind data usually ended at about 

60,000 ft, so from 60,000 to 80,000 ft, if we had no wind data, 

we linearly extrapolated to zero wind speed at 80,000 ft and 

above. The “filtered” wind profile resulted from this process. 

The above phases of flight were flown “open loop”, i.e., only 

the Atlas autopilot was in control. The Centaur guidance loop 

was not closed until BECO + 8 sec. A conceptual filtered wind 

is shown in Figure 6. A real filtered wind in pitch is shown in 

Figure 7. 

Figure 4.—Pitch Trajectory Shaping.

Figure 5.—Yaw Trajectory Shaping.

INTEGRATED HEATING

:

Pitch attitude

:

ZERO YAW VELOCITY HEADING

(SAME HEADING AS IF NO YAW

WERE PERFORMED)

Yaw attitude

NASA/TM—2015-218752 5 
Figure 6.—Pitch and Yaw Wind Profiles Versus Altitude.

Figure 7.—Example of Real Filtered Wind in Pitch Plane.

4.2 Altitude Segments

The next task was to break the altitude span into intervals, or 

“segments”. Over each interval, the filtered wind zero angle of 

attack history would be calculated, and then approximated with 

a polynomial fit. At first we tried linear fits, but the residual 

angles of attack were too large. Then we tried a second order 

polynomial, which reduced the residual angles of attack substantially, i.e., it gave a much better fit. When we tried third 

order fits, there was little improvement over the second order, 

so we decided to use second order polynomials over each interval because they were simpler and had fewer coefficients to be 

transmitted. Two second order polynomials, one in pitch and 

one in yaw, were used to define the desired vehicle attitude over 

each of 11 preselected altitude segments. The altitude intervals 

selected for segmentation varied. The shortest interval was 

5,000 ft over the 30,000 to 50,000 ft altitude range where dynamic pressures were high and could induce large angles of attack and high loads. The coefficients of the polynomials were 

called “steering terms.” The routine that designed the steering 

Pitch Plane Yaw Plane

0

Altitude, ft

Wind Speed 0

80K

Filtered Wind

Measured Wind

NASA/TM—2015-218752 6 
terms was called “Pipeline”. Table 2 illustrates the intervals. 

Figure 8 illustrates the zero angle of attack profile as approximated by polynomials. Note that the polynomials were attitude 

versus altitude, not rate versus time as mentioned earlier. Actually, we used “relative altitude”, which zeroed at the start of 

each altitude segment, and we required attitude continuity at the 

beginning of each segment (Figure 9). This approach required 

only 66 coefficients (11 segments, with constant, linear, and 

quadratic coefficients for each, both pitch and yaw) or “steering 

terms,” to be loaded into the flight computer, and verified for 

transmission accuracy. We tried very hard to keep the number 

of coefficients to a minimum because of the significant concern 

about transmitting flight critical constants to the flight computer 

very near (sometimes only a few minutes) before launch. We 

went through exhaustive testing to absolutely prove our ability 

to do this repeatedly and reliably through the use of check sums, 

check figures, and parody checks. All the coefficients were 

checked prior to upload into the flight computer, and then

downloaded again to verify accuracy.

Since the first use of ADDJUST was on AC-30, Pioneer 11 

to Jupiter, a NASA Ames Research Center payload, Hans Mark, 

Ames Center Director, asked the Lewis Director, Bruce Lundin, 

for an all-day briefing on this thing called “ADDJUST.” 

Jack Estes and I had agreed from the start that, although we had 

different backgrounds and responsibilities for ADDJUST, we 

would both learn every aspect of the program. This turned out 

to be fortunate for me, since Dr. Mark wanted the briefing on a 

day which Jack was not available. After conducting an ~ 8 hr 

grilling (down to details, such as why we used a second order 

polynomial fit), Dr. Mark returned to Ames very satisfied and 

confident in ADDJUST. (In about 1978, the Space Transportation System (STS) program also came to Lewis to understand 

how ADDJUST worked. They were very uneasy with transmitting critical data to the flight computer so close to launch, so 

they elected not to incorporate such a “risky” technique. But 

only a few years into the program, they also started to scrub for 

flight winds, so they eventually, reluctantly adopted a similar 

approach.) Typical coefficients are shown in Table 3. 

TABLE 2.—ADDJUST PIPELINE ALTITUDE SEGMENTS

[11 segmented polynomials (pitcha and yawb)] 

Range of altitudes,

ft

Set number of

polynomial 

steering terms

Description

0 to 1,200 ----- Vertical rise after liftoff

1,200 to 8,000 1st Trajectory shaping (control section)

8,000 to 16,000 2nd Zero angle of attack phases

16,000 to 24,000 3rd

24,000 to 30,000 4th

30,000 to 35,000 5th

35,000 to 40,000 6th

40,000 to 45,000 7th

45,000 to 50,000 8th

50,000 to 60,000 9th

60,000 to 80,000 10th

80,000 and beyond 11th

a

θP = P0(I) + P1(I) ∆h + P2(I) ∆h2

b

θY = Y0(I) + Y1(I) ∆h + Y2(I) ∆h2

TABLE 3.—SET OF TYPICAL ADDJUST PITCH AND YAW POLYNOMIAL COEFFICIENTS

66

Steering

Terms

NASA/TM—2015-218752 7 
Figure 8.—Pipeline’s Polynomial Fit Technique.

Figure 9.—Polynomials Versus Relative Altitude

4.3 The Wind Monitoring Process

The wind monitoring and ADDJUST processes are summarized in Figure 10 and Figure 11. The cycle, which was repeated 

several times on launch day, began with the release of a weather 

balloon, or usually a pair of balloons, by the U.S. Air Force 

weather team in Florida. These balloons returned wind speed 

and direction data as a function of altitude, as well as atmospheric properties. The wind profiles were transmitted to GD 

in San Diego, and Lewis in Cleveland, for analysis. The zero 

angle of attack profile and the associated polynomial steering 

coefficients were calculated in San Diego by the ADDJUST 

program. These coefficients were then sent to Cleveland for 

verification and simultaneously to the Centaur ground computer 

at Launch Complex 36 for potential loading into the flight computer at a later time. The ADDJUST operational process is 

shown in Figure 11. 

Δ

NASA/TM—2015-218752 8 
Figure 10.—ADDJUST Winds Monitoring.

Figure 11.—ADDJUST Operational Process.

NASA/TM—2015-218752 9 
ADDJUST started with the raw, unfiltered wind profile, and 

then ran the data through filters explained earlier. The filtered, 

or “design” wind was then used to calculate the zero angle of 

attack trajectory, the polynomial approximations for each altitude segment, and polynomial coefficients for both pitch and 

yaw planes. These 66 coefficients (called P’s and Y’s) were then 

scaled properly for the Centaur Digital Flight Computer (DCU), 

transmitted to the Centaur ground computer at Complex 36, and 

then uploaded to the flight computer if required. They were also 

sent to NASA Cleveland for subsequent validation. We were 

always very aware of the potential for transmission errorsin this 

process, so we took great precautions to make sure the data was 

sent correctly through the use of check figures, check sums, and 

parody checks, similar to verifying the flight computer loading 

as described earlier. I don’t recall ever having problems with 

transmission errors, although we had frequent problems with 

losing the phone lines from Florida to Cleveland and to San Diego. All the data was sent over phone lines. At first, we had to 

use government lines, which were plagued with problems. 

Soon, we said that we needed to use more reliable commercial 

grade lines, at a transmission rate of 300 baud. (One person 

commented that transmission was so slow it was almost possible to see the bits coming out of the phone receiver!) When we 

went to commercial lines, the phone company warned us that if 

we ever tried to launch on Mother’s day, we may not be able to 

get a line. I don’t recall that we ever launched on Mother’s day.

All of this activity was coordinated by Lewis personnel in the 

tiny “Wind Room” behind the Launch Complex 36 Mission Director’s Center in Hanger AE. 

Once the P’s and Y’s and the actual, measured wind profile 

(not the filtered wind) were loaded into the 6 degree of freedom 

(6 DOF) simulations in San Diego and Cleveland, then the process of computing the resulting loads, control authority, and 

many other mission parameters took place, including automated 

comparison with predetermined allowables for each. This 

whole process took about 1 hr. Since the balloons needed an 

hour to reach the correct altitude in the first place (typically 

around 60,000 ft, if they didn’t burst, freeze up, or blow over 

the horizon first), this meant the measured wind was about 2 hr

old by the time the vehicle flew through it. We examined using 

laser and/or Doppler scans in lieu of balloons because they were 

nearly instantaneous, but because of technical issues, we stayed 

with balloons. This is still true today for Atlas V.

4.4 Mission Acceptance Criteria 

Even though successfully negotiating the flight winds 

was absolutely critical, as mentioned earlier, ADDJUST also 

verified that all equally critical trajectory criteria were met to 

ensure mission success: 

• Structural loads

• Control capability

• Nose fairing temperatures

• Angles of attack, pitch and yaw

• Integrated heating

• Product of dynamic pressure and angle of attack (Q-Alpha) and sideslip (Q-Beta) at jettison events

• Angular rates and accelerations, pitch and yaw

• Performance to Centaur target orbit 

• Range safety boundaries

Trajectories resulting from each ADDJUST design were appropriately scaled and transmitted directly to Range Safety at 

the Eastern Test Range (ETR) for immediate display for the 

Range Safety Officer. Initially, the displays were pen on paper. 

Later they became cathode ray tube (CRT) based. None of these 

constraints was ever violated by any ADDJUST simulations on 

launch day.

4.5 Loads Overview 

Loads during maximum aerodynamic loading region (typically 30,000 to 50,000 ft) were caused by: 

• Steady winds, which were a function of trajectory and 

wind profile

• Axial acceleration

• Drag, which was a function of trajectory shaping and 

wind profile

• Gusts, which were short term wind changes not included 

in the wind profile

• Wind persistence, the variation in wind profile as a function of time

• Buffett, which was treated like random loads 

• Dispersions, some of which were variations in wind 

measurements, trajectory, propulsion system, mass properties, and aerodynamics 

In the above list, the first three had to be calculated on launch 

day using predetermined coefficients. The last four could have

been calculated well in advance of launch day. A 1976 study 

led to updated criteria for gust, persistence, and dispersion 

loads, and this was implemented and used for updated 

Atlas/Centaur flight wind monitoring criteria. Structural factors 

of safety are shown in Table 4. These safety factors were 

intended to account for the inability of analysts to perfectly 

NASA/TM—2015-218752 10
TABLE 4.—ADDJUST FACTORS OF

SAFETY AND OTHER CRITERIA 

Vehicle Station 

(Centaur) 

Time

(seconds 

after 

T = 0)

Ultimate factor

of safety

Buckling 

criteria at 

limit 

load 

Buckling 

criteria at 

ultimate 

load Axial 

load 

Bending 

moment

Centaur 

(tank skin)

219 to 409 0-100 1.10 1.25 Onset 180

Centaur 

(rings)

219 and 412 0-100 1.10 1.25 None None

N/F All 0-100 1.10 1.25 None None

Atlas 

(tank skins)

674 to 819 0-100 1.10 1.25 Onset 180

calculate loads, load paths, strengths, etc., or for overly simplified analytical techniques.

ADDJUST calculated two ratios which were used as principle criteria for launch. The Capability Ratio (CR) was a modification of the stress design-limit interaction ratio and was the 

sum of two quotients: the applied-to-limit bending moments 

with zero axial load; and the applied-to-limit axial load with 

zero bending moment. It was evaluated at various critical stations along the length of the launch vehicle. The Engine Ratio 

(ER) was the ratio of predicted-to-allowable engine gimbal angle for the Atlas booster engines.

CR and ER were calculated at each time for each vehicle longitudinal location, or station. For historical perspective, it 

should be noted that whether the CR or ER was the predominant 

constraint was very vehicle dependent. For example, for the Atlas/Centaur the CR was always the constraint, but for 

Thor/Agena the ER was always more critical.

The highest CR or ER encountered at any time or station was 

used in the above calculation for “GO” or “NO-GO” CR ≤ 1.0 

and ER ≤ 1.0 are required for a launch “GO.”

4.6 Wind Persistence

The wind the vehicle actually encountered in flight was not

identical to any wind previously analyzed. It would have 

changed even relative to the wind measured as close to launch 

as possible. Even small wind changes could have induced significant pitch and/or yaw loads. This inevitable change had to

be addressed with a “persistence allowance.” The nominal 

launch day balloon release schedule is shown in Table 5. The 

day before launch, the first pair of balloons (the System Check 

balloons (Ref. 3), not shown in Table 5) was launched primarily 

to verify readiness of the entire balloon release and ADDJUST 

system. On launch day, four pairs of balloons were released per 

the schedule. The reserve balloons were released primarily to 

rehearse the system for later in the day. ADDJUST designed to 

each pair, but the design was not loaded into the flight 

TABLE 5.—LAUNCH DAY BALLOON RELEASE SCHEDULE

Ballon pair Release time, 

min

Pitch and yaw 

steering design

Reserve L–370 Yes 

Secondary L–265 Yesa

Primary L–145 Yesa

Contingency L–90 Nob

a Loaded into flight computer

b Except on hold

computer. The secondary and primary designs were loaded. The 

contingency data was not loaded unless we were in a launch 

delay, and it was used to assess the projected CR/ER increase 

for extending the launch into a protracted window. The window 

would close when the CR or ER were calculated to exceed a 

value of 1.0. (See discussion below). The contingency data 

were also used for post flight analysis purposes. As an example, 

Figure 12 and Figure 13 show the smoothed wind and measured 

wind for the same launch day, March 26, 1987, both in pitch 

and yaw, for the secondary and contingency balloons.

The structural capability ratio, CR, was always the most critical factor for Atlas/Centaur (see Sec. 4.5), i.e., it was the parameter always closest to its limit, and the factor on which a 

launch “Go/No Go” was based. We needed to calculate a “persistence allowance” for the CR. That is, statistically, how much 

should we allow for the CR to rise to account for the fact that 

our last measurement, based on the primary balloon sounding, 

would be more than 2 hr old by the time the vehicle actually 

flew through the wind? We initially analyzed 150 historical balloon pairs released from ETR from 1965 to 1972, and released 

about 2 hr apart to approximate the launch day time lag discussed above. We designed an ADDJUST profile for the first 

balloon in the pair, and then analytically flew that profile 

against the second balloon data to see how much the CR had 

changed. We also analyzed numerous wind pairs that had actually caused past launch delays. Had ADDJUST been available, 

all would have been “GO.” Finally, we examined synthetic 

wind pairs and other profiles specifically designed to “stress” 

the system. Each time, we executed a complete ADDJUST design cycle for the first balloon of the pair and calculated the CR, 

as well as all the other mission acceptance criteria. Using the 

ADDJUST profile designed for the first balloon, we flew this 

profile against the second balloon’s measured wind profile and 

again calculated the CR and all other parameters, noting the 

changes from the first balloon results. We then performed a statistical analysis on the resulting distribution of the changes and 

calculated a 3 sigma value for changes in CR and ER. This resulted in a CR persistence allowance of about 0.06/hr, or six 

“points/hr” (highly vehicle dependent). This factor was also 

NASA/TM—2015-218752 11
used to predict when an extended launch window would close 

based on expected CR/ER limits. If the window were long 

enough, a balloon pair later than the contingency pair would be 

launched. Results showed that the average increase in calculated loads for ADDJUST cases was about what had been 

experienced in the past for predesigned (i.e., non ADDJUST) 

steering terms. This indicated that ADDJUST design was not 

overly sensitive to lack of wind persistence. Historically, for 

Atlas/Centaur, CR was always much more critical than ER. In 

fact, for that vehicle it was always the most critical parameter.

Figure 12.—Secondary Balloon Wind Profiles.

Figure 13.—Contingency Balloon Wind Profiles.

NASA/TM—2015-218752 12
4.7 NASA Lewis Independent Verification 

And Validation 

The primary purpose of the Lewis IV&V was to independently calculate and verify all the mission acceptance criteria (i.e., CR, ER, performance, range safety, etc.). We ran inhouse 3D and 6D simulations, completely independent from 

GD. Because of extensive (over many years) prelaunch simulation comparison and calibration, Lewis and GD would always 

agree to within 0.01 (1 “point”) on CR. If either capability went 

down on launch day, the other could issue the “GO” or “NO 

GO.” The decision was always “NO GO” if either exceeded 

1.0. To accommodate ADDJUST and its potentially very compressed time frames if we were late in the countdown, Lewis 

undertook a major upgrade in its IV&V hardware and software 

capabilities for data processing and analysis. We did not independently calculate the ADDJUST steering terms, although 

that could have been done. It was not a priority.

While GD calculated ADDJUST steering terms, Lewis first 

ran the previous ADDJUST design through the current, measured wind. Next, we ran the current wind through the backup 

matrix of 10 pitch and 10 yaw programs, searching for a “GO” 

set (after 1972, we rarely found one). This effort was valuable 

because the backup sets also resided in the Centaur ground 

computer at Launch Complex 36 and were not subject to potential cross-country data transmission breakdowns. As it 

turned out, these communications breakdowns were actually 

infrequent and they never prevented us from eventually 

transmitting the coefficients. We never needed a backup 

choice with ADDJUST. Lastly, Lewis validated the current 

ADDJUST design through the current wind.

4.8 Flight-Measured Angle of Attack

The next several charts (Figure 14, Figure 15, and 

Figure 16) present the flight-measured angle of attack data for 

three flights, as measured by a differential pressure sensor on 

the nose cap. Each set shows the angle of attack history for 

the critical period of flight for pitch and yaw (P and Y), and 

the root sum square (RSS) of the two. The first set was for 

AC-26, launched on December 19, 1971. The solution was 

selected from 10 predesigned P and Y steering sets. The RSS 

of P and Y angles of attack are about 2.0°. Not great, but good 

enough for a “GO.” The second set was for AC-27, launched 

on March 2, 1972. The solution for this flight was selected 

from 10,000 predesigned P and Y steering sets. The RSS of P

and Y angles of attack are between 1.5° to 2.0°. This was good 

enough for a “GO,” but we had scrubbed for three previous 

days because the prelaunch search for a solution was too complicated and took too long. This was the flight that led to the 

birth of ADDJUST. The last set was for AC-30, launched on 

April 5, 1973. This was the first use of ADDJUST. The charts 

show the best match yet for zero angles of attack in both pitch 

and yaw, with an RSS of about 0.5°, resulting in a “GO” on 

the first attempt. This reduced angle of attack led directly to 

improved launch availability.

Figure 14.—AC-26 Flight Angle of Attack (No ADDJUST)

NASA/TM—2015-218752 13
Figure 15.—AC-27 Flight Angle of Attack (No ADDJUST).

Figure 16.—AC-30 Flight Angle of Attack (First ADDJUST Usage)

NASA/TM—2015-218752 14
Figure 17.—Launch Availability Improvement with ADDJUST.

4.9 Launch Availability

Launch availability is the percentage of days in a year (expressed as a decimal) for which prelaunch analyses predict a 

“GO” for flight winds (i.e., launch availability of 0.9 meant a 

predicted “GO” for 90 percent of days). Frequently, launch 

availability is calculated for each month. The goal of 

ADDJUST was to yield a launch availability in the winter 

months of at least 90 percent. The resulting launch availability 

is shown in Figure 17. As can be seen, where the winter 

months previously had yielded a launch availability of only 

55 percent, with ADDJUST it went to nearly 100 percent. 

The ADDJUST system cost about $250,000 to develop. In 

return, it saved countless scrubs at more than $1 million per 

day. Including its first use on AC-30, ADDJUST flew on 

44 Atlas/Centaur and 7 Titan IIIE/Centaur flights through 

1998. Even allowing for persistence, ADDJUST always found 

a solution on the very first attempt. Through the end of the 

Centaur program at Lewis in 1998, we never scrubbed for 

flight winds again!

5.0 Conclusions

ADDJUST was the first use of steering programs derived 

and uploaded in near real time, and it met or exceeded every 

one of its design goals. It is a remarkable achievement and set 

the standard for near real time, reliable communications of 

flight critical software. It prevented countless scrubs due to 

flight winds, avoiding the associated risks. ADDJUST was 

flown on 51 Centaur flights from 1973 until 1998, and always 

enabled a “GO” on the very first attempt, resulting in a year 

round launch availability of nearly 100 percent. In this period, 

we never scrubbed for flight winds again. Even its acronym 

(conceived by Frank Anthony of GD) was remarkable, and 

remains one of the most ingenious and descriptive ones I can 

recall. Participating in its development was one of the highlights of my career. Working with Jack Estes at Lewis, and 

with Dan Swanson and his dedicated team at GD, showed me 

what a small, highly motivated team could accomplish, even 

with a very short schedule and extreme pressure to produce. I 

always felt that it was an honor to be asked to work with these 

fine gentlemen.

Reference

1. Swanson, D. C., “ADDJUST-An Automated System for 

Steering Centaur Launch Vehicles in Measured Winds,” 

7th Conference on Aerospace and Aeronautical Meteorology and Symposium on Remote Sensing from Satellites, 

Melbourne, FL, American Meteorology Society, #A78-

14991, Nov. 1976.

2. Nieberding, J.J., McAleese, J., “Historical Perspective – 

Wind Biased Steering,” Unpublished PowerPoint Presentation, NASA Langley Ares I-X Team, July 10, 2007.

3. “Centaur D-1A Systems Summary,” General Dynamics 

Convair Aerospace Division, Report No. GDCA BNZ72-

020, Contract NAS3-13514, San Diego, CA, Sept 1972.

4. “Countdown Summary, Launch/Hold Criteria, and Flight 

Events, CRRES Mission, AC-69,” General Dynamics 

Commercial Launch Services, Report No. GDSS-ACE87-001, Contract NAS3-23330, San Diego, CA,July 1990.

NASA/TM—2015-218752 15