# Presentation: 035181

## ON THE FEASIBILITY  OF A NEW FRONTIERS CLASS SATURN PROBE MISSION 

- ON THE FEASIBILITY  OF A NEW FRONTIERS CLASS SATURN PROBE MISSION

- by
**Tibor S. Balint ***– study lead*** **& the** Saturn Probe Study Team **
- Presented at the4th International Planetary Probe Workshop
- Pasadena, California
- June 27-30, 2006

- TSB.JPL.05

- TB

## Acknowledgements

**Acknowledgements**

**Saturn Probes Study Team (SPST):**
- Doug Abraham 	– DSN / Telecom (JPL)
- Gary Allen 	– Probe descent (Ames)
- Dave Atkinson 	– Science (U of Idaho)
- Tibor Balint 	– *Study lead*, Architectures, Power (JPL)
- Rob Carnright 	– Trajectory visualization (JPL)
- Bill Folkner 	– Telecom, Architectures (JPL)
- Sergey Gorbunov	– Probe CAD (NASA Ames)
- Helen Hwang 	– TPS, costs (NASA Ames)
- Anil Kantak 	– Telecom (JPL)
- Theresa Kowalkowski – Trajectories (JPL)
- Try Lam 	– Trajectories (JPL)
- Ed Martinez 	– TPS, costs, E/D (NASA Ames)
- Dave Morabito 	– Telecom (JPL)
- Bill Smythe 	– Science, Instruments (JPL)
- Tom Spilker 	– Architectures, Attenuation, Science (JPL)
- Nathan Strange 	– Trajectories, Architectures (JPL)
- Bill Strauss 	– Probe entry / descent (JPL)
- Mike Tauber 	– TPS, E/D (ELORET Corporation)
**Study Sponsors:**
- Curt Niebur 	– NASA HQ
- James Cutts 	– 4X Chief Technologist (JPL)
- Gregg Vane 	– 4X Program Manager (JPL)
**Additional thanks for their support and input to: **
- Sushil Atreya (science); Jennie Johannesen (trajectories);

## Caveat

- This presentation focuses strictly on
- Science goals and strawman payload
- Trajectories
- Telecom / attenuation
- Atmospheric entry,  descent and TPS issues
- Communications
**The presentation does NOT provide a full systems engineering description**
- It is assumed that the operation for the Saturn flyby mission concept described here would last only for about 5 hours, therefore, the power requirements on the flyby spacecraft would be satisfied by the combination of solar power generation and batteries. Longer missions at this distance from the Sun would likely require internal power sources, such as RPSs.
- In this study:
- For Power:
- We could assume a Juno class solar panel configuration
- For Thermal Management:
- On the probes we would likely require RHUs for component heating
- The views and opinions expressed here are those of the author and does not necessarily represent official NASA policy.

## Overview

**Introduction:**  How does the Saturn Flyby with Shallow Probes mission  fit into the SSE Roadmap?
**Questions to be answered in this presentation:**
- 1: What are the Science Objectives & Instruments?
- 2: What is the mission “wish list” & a representative mission architecture?
- 3: How to get from Earth to Saturn?
- 4: What is an “ideal flyby” at Saturn?
- 5: Can we / How to do microwave radiometry?
- 6: Any issues with atmospheric entry and descent?
- 7: Can we communicate back the probe data?
- 8: Can we do Direct to Earth communication from the probe?
**Conclusions**

- TB

## IntroductionSaturn Probes & the 2006 SSE Roadmap

**Introduction****Saturn Probes & the 2006 SSE Roadmap**

- The **2006 SSE Roadmap** is currently under way
- It identifies a **New Frontiers Class Saturn Flyby ****with Probes Mission** as one of the options for the next New Frontiers opportunity
**The goal is to demonstrate that we can do this**

- Ref: Solar System Roadmap 2006

## What are the Science Objectives?

- The key science objectives that would be addressed by the Saturn Probe mission are:
**Origin and Evolution** **–** _Saturn atmospheric elemental ratios_ relative to hydrogen (C, S, N, O, He, Ne, Ar, Kr, Xe) and key isotopic ratios (e.g., D/H, 15N/14N, 3He/4He and other noble gas isotopes), _gravity and magnetic fields_; _He relative to solar, Jupiter_. [P, C]
**Planetary Processes**** –** _Global circulation, dynamics, meteorology_. _Winds_ (Doppler and cloud track), _interior processes_ (by measuring disequilibrium species, such as PH3, CO, AsH3, GeH4, SiH4). [P, C]

***Key: Comparative planetology of well-mixed atmospheres of the outer planets is key to the origin and evolution of the Solar System, and, by extension, Extrasolar Systems (Atreya et al., 2006)***

- Ref: Atreya, S. K. et al., (2006) Multiprobe exploration of the giant planets – Shallow probes, Proc. International Planetary Probes Workshop, Anavyssos, 2006.

- Ref: Dave Atkinson

*NASA – Cassini: PIA03560: A Gallery of Views of Saturn's Deep Clouds *

## Typical Science Instruments Expected for a Saturn Probes & Flyby S/C

- This **might be** an **oversubscribed** strawman payload set
- The actual number of instruments would be dictated by the final mission cost, fixed at $750M FY05 for a NF mission *(Juno)*
**We assumed the same instrument sampling rate per distance traveled as used on the **_**Galileo probe**_

| Shallow Probe to 10 bars |
| --- |
| ASI 	– Atmospheric Structure |
| NEP 	– Nephelometer |
| HAD 	– Helium abundance |
| NFR 	– Net flux radiometer |
| NMS 	– Neutral mass spectrometer |
| LRD /EPI 	– Lightning / Energetic particles |
| ARAD 	– Ablation monitor – on TPS |
| DWE 	– Doppler wind experiment |
| OPH 	– Ortho-Para Hydrogen |
| TLS 	– Tunable laser spectrometer |
| IMG 	– Imaging |
| MWR 	– Microwave radiometer |

| Flyby |
| --- |
| GRV 	– Gravity mapping |
| MAG 	– Magnetometer |
| SSI 	– Imaging |
| DWE 	– Doppler Wind Experiment |

- Ref: Dave Atkinson, Bill Smythe (with comments from Sushil Atreya)

## What is the mission “wish list” & a typical mission architecture?

_**Science community “wish list” for mission success:**_
- Saturn Flyby with two (2) shallow probes to 10 bars
- Microwave radiometry to ~100 bars
- Probe 1: equatorial probe (0°), and
- Probe 2: mid-latitude probe (-45°)
_**Representative mission architecture assumptions:**_
- Identical Galileo class probes; Spin stabilized
- (a) Chemical propulsion or (b) SEP (to get there)
- Multiple Gravity Assist (to increase delivered mass)
- Probes Released 6 months before Saturn flyby (the same way as Galileo did it)
- Go between F and G rings ~2.34-2.82 Rs  (2.634 Rs – where Cassini passed, to avoid ring particles)
- UHF communication between probes and flyby S/C
- X-band from Flyby S/C to Earth
- Power sources considered in this study:
- On flyby S/C: LILT-solar / batteries
- On probes: primary batteries

- Ref: T. Spilker, T. Balint, N. Strange, W. Folkner, & the Saturn Probe Study Team, with input from S. Atreya and D. Atkinson on science rationale

- TB

## How to get from Earth to Saturn? Chemical & SEP Options for the Same Representative Trajectory

**How to get from Earth to Saturn?**** ****Chemical & SEP Options for the Same Representative Trajectory**

**2015 Launch – 6.3 years flight time** – **EEJS Gravity Assist Trajectory**** **
- For the **same flight time** the **SEP** system delivers approximately **30% more** mass to Saturn for our case; or the same mass at a smaller L/V

**Chemical**

**SEP**

- Ref: Theresa Kowalkowski, Try Lam

## What is an “ideal flyby” at Saturn? How to do microwave radiometry?Saturn Arrival Geometry – Passing Through the F & G Ring Gap

**What is an “ideal flyby” at Saturn? How to do microwave radiometry?****Saturn Arrival Geometry – Passing Through the F & G Ring Gap**

*NOTE: Range & elevation calculations are made with respect to a fixed point rotating with Saturn*

- Nominal Probe1 Transmit Period

- Nominal Probe2 Transmit Period

- Ref: Theresa Kowalkowski, Try Lam

- Note: these results are NOT optimized!

- These distances (ranging from 100,000 to 200,000 km) might be too large for microwave radiometry, therefore, for this study_**we placed the radiometers on the probes**_!thus, making the MR measurements before probe entry.

- Flying inside the rings:	good distance / short visibility, telecom window
- Flying outside the rings:	too far / but long telecom window

- Probe 1

- Probe 2

## Any issues with atmospheric entry and descent?Probe Entry / Aeroshell 

**TPS mass-fractions**
- For low-latitude retrograde entries, about same as Galileo probe (~50% including margins, etc.)
**For prograde entries, about 30% less than Galileo**
- Nearly same for big and small probes if m/CDA same
**Max. heating rates** and **max. g** about **35% of Galileo**
**Heating pulse about 2.5 times longer** (atm. density scale height about 2.5 larger at Saturn than Jupiter)

- Saturn probes have **less ablation**, but need more insulation
**Time to parachute deployment** is about **5 minutes**
- Time to **descend to 10 bar** altitude is about **2 hr. 26 min**. (using Galileo parachute size)
*(note: very similar to the independent calculations by Bill Strauss)*

| Entry
direct. | Latitude
deg | Rel. entry
 V, km/s | Max diam.,m | Entry mass,
kg | Max. heat 
rate*,
kW/cm2 | Forebody TPS mass fraction | Est. total TPS
mass fraction+ | Max. decel.,
g |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Pro. | 6.5 | 26.8 | 1.265 | 335 | 2.66 | 0.235 | 0.258 | 43.6 |
| Pro. | 6.5 | 26.8 | 0.8 | 130 | 3.27 | 0.243 | 0.267 | 43.3 |
| Pro. | -45 | 29.6 | 0.8 | 130 | 4.44 | 0.256 | 0.282 | 47.7 |
| Pro. | -45 | 29.6 | 1.265 | 335 | 3.67 | 0.248 | 0.273 | 47.9 |
| Retro. | 6.5 | 46.4 | 1.265 | 335 | 21.5 | 0.352 | 0.387 | 76.4 |
| Retro. | 6.5 | 46.4 | 0.8 | 130 | 22.3 | 0.348 | 0.383 | 75.3 |

- Ref: Mike Tauber, Gary A. Allen, Jr.  and Lily Yang

- Note: these table values are given for a flight path angle of -10°, whereas the trajectory calculations on Page 16 are givenfor -8°. At -8° the equatorial retrograde entry results in a TPS mass fraction that exceedsthat of the Galieo probe.

- (+ zero margins)

## Any issues with atmospheric entry and descent?Probe Descent time vs. Altitude Down to 30 bars

**Any issues with atmospheric entry and descent?****Probe Descent time vs. Altitude Down to 30 bars**

- If **free fall begins at pressure of 1 bar**, it will take **~70 minutes** from entry **to** reach **10 bars**
*For better **probe stability**, the freefall phase could be replaced with **descent with a smaller second parachute*
- If the descent is **entirely on the parachute**, it will take **~2.5 hours to** reach **10 bars**

- Ref: Bill Strauss / Independently confirmed by Gary Allen (both using a Saturn Atmosphere Model by G. Orton)

- TB

**0 km ********1 bar**

## Can we communicate back the probe data?Attenuation in Saturn’s Atmosphere

**NOTE: This is discussed in detail ****by Tom Spilker in his presentation**
**One of a kind computer code** was developed **by Tom Spilker** specifically for this study to calculate attenuation for Saturn’s atmosphere
- Findings:**Attenuation at 10 bar**
**UHF: ~1.5 dB** (~1.2 dB + margin)
**S-band**: ~31 dB (**No link!**)
- These results feed directly into the telecom link budget calculations, and also impact Direct-to-Earth feasibility
- Saturn atmospheric model for Tom’s calculations was provided by Glenn Orton
**Scale height is ~2x that of Jupiter’s**** **~45 km at the pressures of interest
- However, **no radiation** environment

- Ref: Tom Spilker

**UHF: 401 MHz**

**S-band: 2.065 GHz**

## Can we communicate back the probe data?Saturn Probes Proximity Data Rates at UHF

_**From Flyby S/C to Earth**_
- The data from the two probes would be relayed back
- to Earth at X-band using a 35-W TWTA and 3-m diameter
- antenna to a 34-m antenna within the first two hours of
- a single tracking pass

- Ref: David Morabito, Anil Kantak and Arv Vaisnys

- Carrier lock threshold

_**From Probe to Flyby S/C**_
- Point design resulted in a lower data rate, than preliminary calc.:
- _Probe__	__data rate__	__(volume)_
*Probe 1:**	*1024 bps (~3.7 Mb)
*Probe 2:**	**  *512 bps (~1.9 Mb)
**Still sufficient** to upload the data to the flyby S/C, including the additional ~1.5Mbits stored from the Microwave Radiometry and piggybacked with the normal probe data.

- With the current trajectories, studied here, **neither probe has line-of-sight to Earth** during atmospheric descent
**Flyby would be occulted ± 20 minutes **around Probe 2’s prime transmit time
- Consequently, we assumed **store and dump** operation

## Telecom: DTE Communications:Direct-to-Earth from Saturn using UHF and S-band

**UHF Case**

**S-band Case**

- Notes – additional atmospheric attenuation makes               S-band prohibitive; For Arecibo, Saturn is outside of the declination range

**To Orbiter/Flyby**

**To Orbiter/Flyby**

**Direct to Earth**

**Direct to Earth**

- To Orbiter/Flyby

- Direct to Earth

- Antenna and Telecom power on probe would be limited, and not sufficient to provide Direct to Earth communication; Probe size would limit scaling up antenna & power.

- Ref: David Morabito

## Conclusions

- A proposed Saturn Flyby with Shallow Probes mission is in line with New Frontiers requirements
- The actual cost would be based on the given point design with a suitable instrument suite
- This type of mission would not require technology development and could leverage from flight heritage, e.g.:
- Galileo probe design/instruments; Juno solar panels and microwave radiometry; Electra UHF transceiver from the Mars program
- SEP trajectory option is comparable in cost to Chemical option
- For the same delivered mass SEP uses a smaller L/V, offsetting SEP cost
- Thermal Protection System:
- TPS mass fraction: For retrograde entry: Galileo-like; For prograde: ~30% less
- For prograde entry the heating rate is at least an order of magnitude less than at Jupiter, but the heat pulse is longer
- entry latitude is not limited by TPS
- UHF communication
- From probes to flyby is feasible (including probe + radiometry data)
- Direct-to-Earth communication is not NOT feasible for the expected data rate
- Only the (not yet available) SQ KM array would be capable of any DTE data return, and only while conditions are favorable at UHF (link along vertical)
- S-band links would be prohibitive for DTE, for this mission concept, due to significant atmospheric attenuation.

## The End

## How to Reduce Mission Cost?

_**Assume / use**_ mission, instrument and design _**heritage**_ when possible, for example:
- Galileo probe (instruments, power system, descent module)
- TPS (use existing materials (carbon phenolic), don’t plan to restart facilities)
- Juno (LILT solar panels, microwave radiometer)
- Electra (telecom system)
_**Minimize**_ science _**instruments or instrument cost**_
- Descope towards minimum science requirements
- Allow for contributed instruments
_**Simplify**_ mission _**architecture**_
- Shorter flight times reduce operations costs
- Use a flyby instead of an orbiter
- Drop down in Launch Vehicles (by minimizing spacecraft mass)

- TB

## Background info

- TB

## Galileo Probe Science Instrument Accommodation

- Note: Instrument suite sizes pressure vessel mass / volume / thermal

| Instrument | Mass  | Power  | Bit rate  | Volume  | Special Acc. Requirements |
| --- | --- | --- | --- | --- | --- |
| Atmosphere structure instrument (ASI) | 4.0 kg | 6.3 W | 18 bps | 3100 cm3 | Pressure inlet port; temperature sensor outside boundary layer; 12,408 bits storage |
| Nephelometer (NEP) | 4.8 kg | 13.5 W | 10 bps | 3000 cm3 | Free-stream flow through sample volume; 800 bits data storage; pyro for sensor deployment |
| Helium abundance detector (HAD) | 1.4 kg | 1.1 W | 4 bps | 2400 cm3 | Sample inlet port |
| Net flux radiometer | 3.0 kg | 10.0 W | 16 bps | 3500 cm3 | Unobstructed view 60° cone +/-45° with respect to horizontal |
| Neutral mass spectrometer (NMS) | 12.3 kg | 29.3 W | 32 bps | 9400 cm3 | Sample inlet port at stagnation point |
| Lighting and radio emission detector/ energetic particle detector (LRD/EPI) | 2.5 kg | 2.3 W | 8 bps | 3000 cm3 | Unobstructed 4P Sr FOV; RF transparent section of aft cover, 78° full cone view at 41° to spin axis |
| Total | 28 kg | 62.5 W | 128 bps+ | 24,400 cm3 |  |

*Ref.s: Proc. AIAA’83, 21**st** Aerospace Science Meeting, Jan. 10-13, 1983, Reno, NV & **          Personal communications with Rich Young, February 2005*

*+** including playback of entry data and miscellaneous allocation: 40 bps*

## Galileo Probe Science Instruments

| Instrument | Description |
| --- | --- |
| Atmosphere Structure Instrument
 | Provides information about temperature, density, pressure, and molecular weight of atmospheric gases. These quantities were determined from the measured deceleration of the Probe during the atmospheric entry phase. During the parachute-descent phase, the temperature and pressure were measured directly by sensors extending from the body of the spacecraft. |
| Neutral Mass Spectrometer | Analyzes the composition of gases by measuring their molecular weights. |
| Nephelometer
 | Locates and measures cloud particles in the immediate vicinity of the Galileo Probe. This instrument uses measurements of scatterred light from a laser beam directed at an arm extending from the Probe to detect and study cloud particles. |
| Lightning and Radio Emissions Detector | Searches and records radio bursts and optical flashes generated by lightning in Jupiter's atmosphere. These measurements are made using an optical sensor and radio receiver on the Probe.  |
| Helium Abundance Detector | Determines the important ratio of hydrogen to helium in Jupiter's atmosphere. This instrument accurately measures the refractive index of Jovian air to precisely determine the helium abundance.  |
| Net Flux Radiometer
  | Senses the differences between the flux of light and heat radiated downward and upward at various levels in Jupiter's atmosphere. Such measurements can provide information on the location of cloud layers and power sources for atmospheric winds. This instrument employs an array of rotating detectors capable of sensing small variations in visible and infrared radiation fluxes. |
| Energetic Particles Instrument
  | Used before entry to measure fluxes of electrons, protons, alpha particles, and heavy ions as the Probe passes through the innermost regions of Jupiter's magnetosphere and its ionosphere. |
| Relay Radio Science  Experiments | Variations in the Probe's radio signals to the Orbiter will be used to determine wind speeds and atmospheric absorptions.  |
| Doppler Wind Experiment
 | Uses variations in the frequency of the radio signal from the Probe to derive variation of wind speed with altitude in Jupiter's atmosphere.  |

*Ref: Personal communications with Rich Young, February 2005*

## Trade Elements & Decision Drivers

- Trajectory *(target mission timeframe)*

- Launch opportunity *(mission timeframe)*

- Architecture *(lower cost)*

- Number of probes *(science)*

- Descent module(s) *(simplicity)*

- Approach *(comm, TPS)*

- Descent depth *(science)*

- Telecom Architecture *(physics)*

- Descent mode *(visibility, comm, extr.env)*

- Atlas V 551

**Atlas V 531**

- High thrust direct

- Low thrust direct

- 2015 EVEVEJS

**HT Gravity Assist**

**LT GA**

**EEJS**

- EJS

- Other 2015 +

- Orbiter with Probe(s)

**Flyby with Probe(s)**

- One

- Three

- Polar approach

**Equatorial approach, prograde**

**Two**

- Four or more

**Single descent**

- Two or multiple descents

**Orbiter/Flyby Store and Dump Relay Telecom**

- Direct-to-Earth Telecom

- Parachute only

**Chute 1bars+freefall 10 bars**

- Freefall to 10 bars

**10 bars**

- 200 bars

- Direct

- 20 bars

- Probe size *(heritage)*

**Galileo class**

- Half size (mass)

- Half size (dimensions)

**Trade Elements & Decision Drivers**

**Atlas V 511**

- Atlas V 521

- Atlas V 541

- EVVEJS

- 5 bars

- 50 bars

- 100 bars

- Mission Class ***(key study driver)***

- Discovery Class

**New Frontiers Class**

- Flagship Class

**Eq. approach, retrograde**

- None

## Feasibility Study Objective

**Demonstrate the feasibility of a **
***Saturn Flyby with Shallow Entry Probes***
**mission within the New Frontiers Category **
**in support of the SSE Roadmap**

- TB

- Achieving this can be a tall order, therefore, we may have to take measures to reduce cost

- Ref: CAD by Sergey Gorbunov

- TB

## Science Instruments:Probe Design: Galileo Probe Heritage

| Item / Subsystem | Mass (kg) | Mass Subtotals (kg) |
| --- | --- | --- |
| Deceleration Module |  | 221.8 |
| Forebody heat shield | 152.1 |  |
| Afterbody heat shield | 16.7 |  |
| Structure | 29.2 |  |
| Parachute | 8.2 |  |
| Separation hardware | 6.9 |  |
| Harness | 4.3 |  |
| Thermal control | 4.4 |  |
| Descent module |  | 117.1 |
| Communications subsystem | 13.0 |  |
| C&DH subsystem | 18.4 |  |
| Power subsystem | 13.5 |  |
| Structure | 30.0 |  |
| Harness | 9.1 |  |
| Thermal control | 4.3 |  |
| Science instruments | 28.0 |  |
| Separation hardware | 0.9 |  |
| Probe Total |  | 338.9 |

_**Science Instruments:**_
**(ASI)**
- Atmosphere structure instrument
**(NEP)**
- Nephelometer
**(HAD)**
- Helium abundance detector
**(NFR)**
- Net flux radiometer
**(NMS)**
- Neutral mass spectrometer
**(LRD/EPI)**
- Lighting and radio emission detector/ energetic particle detector

*Ref: Galileo Probe Deceleration Module Final Report, Doc No. 84SDS2020, General Electric Re-entry Systems Operations, 1984*
*AIAA,“Project Galileo Mission and Spacecraft Design”, Proc. 21st Aerospace Science Meeting, Reno, NV, January 10-13, 1983*

## Trajectories:Sequence of Events

**Interplanetary trajectory** description:
**EEJS** (2+ ΔV-EGA)
**~6.3-yr** flight time
- Arrival V∞=9.5 km/s
**Probes released 6 months before entry**
- Probe targeting sequence (begins 180 days before entry)
- Probe1 release
- Targeting maneuver
- Probe2 release
- Divert maneuver

**Probe1** targeted to **0****° latitude**
- Longitude ends up at 140.9°
- Radius is 61,268 km
**Probe2** targeted to **-45° latitude**
- Longitude ends up at 72.8°
- Radius is 58,088 km
**Enters 2 hours after Probe1 entry**
- Crosses ring plane at radius of 480,000 km (outside edge of E-ring)

- Targeting notes
- 10 days between each maneuver
- “Entry” defined as reaching altitude of 1,000 km (oblate Saturn)
- Targeted flight path angle = -8°
**Flyby S/C crosses the ring plane in the ****F & G gap**
- Crosses 60 min. after Probe1 entry
- 150,000 km radius at 0° latitude

- Ref: Theresa Kowalkowski, Try Lam

## Trajectories:Representative Baseline Trajectory

- Probe trajectories were constructed based off a representative trajectory
- EEJS (2+ Earth resonance)
- December 2015 Launch
- 6.3-yr flight time

| Launch Vehicle | Delivered Mass* |
| --- | --- |
| Delta IV - 4050H | 4411 kg |
| Atlas V - 551 | 3073 kg |
| Atlas V - 521 | 2124 kg |
| Atlas V - 401 | 1566 kg |
| Delta IV - 4040-12 |  956 kg |

- *Deterministic and optimal performance values; does not include statistical estimates or a 21-day launch period analysis

- Ref: Theresa Kowalkowski, Try Lam

- The point design allowed us to consider a smaller Launch Vehicle, thus reducing cost

## Trajectories:Delta-V Budget for the Representative Trajectory

- A break down on delivering **~3,000 kg** to Saturn:
- An **EEJS** trajectory with a DSM can deliver ~3,000 kg to Saturn in **6.3 years** on an Atlas-V (551).
- Using SEP the delivered mass can increase by ~1,000 kg for the same flight time, allowing for a smaller launch vehicle, the Atlas-V (521), for the same delivered mass.
- An **EVVEJS** trajectory w/out any DSM can deliver ~3,000 kg to Saturn in 8 years on an Atlas-V (521).

- Accounting for a 21-day launch period the delivered mass is slightly lower than 3000 kg:
- Assuming a main propulsion system with Isp=300 s

- **Note that the “dry mass” calculation does NOT take into account ACS propellant requirements

- Ref: Theresa Kowalkowski, Try Lam

**~10% reduction in delivered mass**
- when the launch window accounts **for a 21 day launch period** instead of the optimal launch day

## How to get from Earth to Saturn?Trajectory Trade Space – Optimal Performance to Saturn for Atlas V

- Ref: Theresa Kowalkowski, Try Lam

- We assessed the trajectory trade space for a 2015 launch opportunity – baselined the 6.3-year cruise

**Mass gain with SEP**

## Telecom: DTE Communications:Direct-to-Earth from Saturn using UHF & Assumptions

**Telecom: DTE Communications:****Direct-to-Earth from Saturn using UHF & Assumptions**

_**DTE Ground assets considered:**_
- 1 SQ KM Array – does not yet exist
- Greenbank 100-m
- DSN Large Array
- Does not yet exist
- Would need upgrading to UHF
- 70-m – would require upgrading to UHF
- 34-m – would require upgrading to UHF
- Arrayed 70-m plus two 34-m’s
- Would require upgrading to UHF
- Phased-up VLA
- Arecibo
- During mission, Saturn declination is outside Arecibo’s range

- Notes – Additional atmospheric attenuation at S-band is prohibitive. For Arecibo, Saturn is outside dec range

- Update Slide with new figures from Dave M.

- Ref: David Morabito

_**UHF Link Assumptions: **_
- UHF 401 MHz Frequency half-duplex
-  6 dB  data channel margin
-  Assume one hour of data acquisition (transmission of data during probe descent)
-  Signal Characteristics (Electra heritage)
-  PSK Bi-phase
-  60 deg modulation index
-  Convolutional (7,1/2) with Reed-Solomon Coding with   convolutional interleaver
-  Probe transmitter/antenna
-  20-W RF (Requires Electra NRE, Jupiter probe assumed 92-W)
-  LGA transmit antenna (boresight along spacecraft axis) assumed nominal gain pattern
-  Assume Earth direction along LGA boresight
-  Assumed probe LGA boresight aligned with local vertical
-  0.5 dB circuit loss (assume single strings on two redundant probes)
-  Assume RF-transparent parachute
-  Pendulum oscillation motion of probe/parachute system not yet accounted for (may lose link during oscillation)
-  Saturn Atmospheric Attenuation
-  1.5 dB along the vertical corresponding to tau = 0.35 (Ref. Tom Spilker provided chart)
-  Saturn Hotbody
-  About 400K at UHF – resultant temperature increase is small (< 5K) at UHF for SQ KM at Saturn-Earth distance
-  Ground Aperture
-  50% aperture efficiency
-  Cooled receiving electronics