From: higgins@fnalf.fnal.gov (Bill Higgins-- Beam Jockey)
Newsgroups: sci.space
Subject: Early Robotic Lunar Missions
Summary: Workshop on Moon orbiters, landers, instruments
Keywords: Moon lunar Griffin SEI resource mapper
Date: 28 Jul 92 14:03:06 GMT
Organization: Fermi National Accelerator Laboratory

[Remember I was complaining about the dearth of information on the
NASA Office of Exploration lunar missions?  Here's my contribution to
filling the gap. Reprinted with permission from *Lunar and Planetary
Information Bulletin* No. 63, May, 1992. --WSH]

         BACK TO THE MOON -- EARLY ROBOTIC MISSIONS                            

by David C. Black and Paul D. Spudis                                            

NASA's newly re-established Office of Exploration is planning several   
small, robotic missions to the Moon within the next three years to
begin the Space Exploration Initiative, the nation's program
to return to the  Moon and journey to Mars. The need for
small, unmanned lunar missions is both technical and
programmatic. To support extended human operations on and
around the Moon we must acquire knowledge about the distribution of 
lunar resources and the detailed characteristics of the surface at
proposed  human outpost sites, and we must learn more about the
gravity field and  global terrain. For the program to succeed,
we must demonstrate that innovative, inexpensive
exploration techniques are feasible and will   produce
quality results.                                                      

  A Workshop on Early Robotic Missions to the Moon was held at the
Lunar and Planetary Institute, February 4-6, 1992, to assess instruments 
that could be used on these early unmanned missions. Instruments 
were evaluated mainly for scientific relevance and quality of the 
dataset that they would return; however, their usefulness in resource 
exploration and processing was also considered.          

  The Office of Exploration has established four themes for early lunar         
robotic missions: resources, terrain--both topography (altimetry) and           
surface morphology (imaging)--gravity, and lander missions.                     

ORBITAL AND LANDED PAYLOADS                                                     

Sixty instrument or mission concept proposals, about equally divided            
between orbital and landed operation, were considered.                          

  The Lunar Exploration Science Working Group (LEXSWG), a standing advisory     
group to the Solar System Exploration Division of NASA's Office of Science      
and Applications (OSSA), has developed a prioritized list of global data        
sets with specific quantitative measurement requirements that are desired       
from lunar orbital missions (see table). The workshop found that there are      
excellent candidate instruments to obtain these datasets. At present, there     
is no prioritized list of data sets expected from payloads landed on the        
lunar surface (although one is being developed by the LEXSWG).                  

   We discussed landed payloads in the context of the proposed "common          
lunar lander," Artemis. Payload capability would be only about 65 kg for        
the first lander, but most proposals anticipate a 200-kg capability, which      
is being investigated for subsequent versions of Artemis. Also, the             
baseline design of Artemis has no provisions for power or communications.       
These engineering constraints did not affect the workshop's assessment of       
the various landed instruments.                                                 

   While landed payloads in general are not as fully developed as orbital       
payloads, a wide and interesting range of concepts offers great scientific      
potential as well as being useful for exploring lunar resources.                

RECOMMENDATIONS                                                                 

We concluded that these missions offer the opportunity to do outstanding        
science, and that there are high-quality instruments that could be flown        
within three years, including landed science as well as orbital science         
instruments.                                                                    

  Flight-ready, new-generation instruments are, in general, not immediately     
available, and some of the more promising instruments that were reviewed,       
while not new in concept, are still at the advanced testing and breadboard      
stages. This is because relatively little lunar instrument development has      
been done during the past decade and a half, so most of the state-of-the-       
art instruments reviewed at the workshop were developed for nonlunar            
missions, or their components have been qualified for spaceflight in other      
contexts. The suite of instruments that we recommend can be flown within        
three years, as long as prompt and adequate funding is made available to        
the instrument teams. The Office of Exploration should take the lead in         
establishing a flight instrument development program.                           

  This instrument situation applies not only to the science payloads, but       
to the resource-utilization payloads that were reviewed at the workshop.        
The maturity of the proposed resource utilization concepts, potentially         
quite useful to achieving the goal of a permanent human presence, is not as     
advanced as those for many of the science instruments; few have even            
breadboard hardware models. As with science instruments, there is a             
critical need for NASA to initiate resource instrument development.             
Resource utilization instruments could be flown soon after more mature          
science instruments, provided that development starts soon.                     

  The workshop also noted a pressing requirement for mobility on early          
landed science missions and that the JPL minirover is relatively mature and     
addresses most mobility needs for early exploration. The Office of              
Exploration should examine whether other engineering solutions could be         
developed quickly enough.                                                       

Orbital Mission 1  Resources                                                    

Three proposed instruments working together can provide global maps of          
lunar chemistry and mineralogy. We believe that given adequate and timely       
resources, flight-ready versions of these instruments can meet a launch         
date within three years. Their combined mass, power, and datarates are          
plausible for orbiters of modest capacity.                                      

  A gamma ray/neutron spectrometer with a germanium detector would provide      
global chemistry with a low resolution footprint (dependent on orbital          
altitude, but greater than 100 km). This is the only instrument that senses     
composition to depths greater than several micrometers. The scientific          
return is very high, but cooling the detector to 70 K poses a challenge.        
Should this preclude a 1995 launch, a similar instrument using a sodium         
iodide detector could provide useful preliminary information until the Ge       
detector is launched later.                                                     

  A soft X-ray fluorescence instrument, to be flown soon on the Alexis          
spacecraft, can detect all major elements with high spatial resolution (1-      
km pixels) to yield far more definitive constraints about regolith              
characteristics, origin, and evolution than was thought possible from an        
orbital mission until very recently.                                            

  A visible-infrared reflectance instrument provides information on             
minerals in surface soils. A full-scale imaging spectrometer collects image     
data in hundreds of spectral channels; thus, each pixel has a single            
spectrum of up to 256 points. If this instrument is not ready for flight in     
three years, a capable multispectral imager (of about six channels) could       
be sent on an early lunar mission. One of these instruments should be part      
of the first suite of instruments; the choice between them is a matter of       
technical readiness. The full-scale imaging spectrometer should be flown as     
early as possible.                                                              

Orbital Mission 2  Terrain                                                      

From the Apollo program, we already have some maps of the topography and        
gravity field of the Moon. However, serious gaps exist in these data in         
both in coverage and quality. Instruments for a second orbiter should           
obtain global gravity and terrain information to support exploration and        
scientific studies.                                                             

  A laser altimeter can collect global altimetry giving us an accurate          
picture of the lunar figure and gross topography of large regions. A number     
of the proposed altimeters have some flight hardware derived from the Mars      
Observer program. Which one to select is purely an engineering issue, as        
long as the instrument meets the LEXSWG requirements (Table 1).                 

  Mapping variations in the gravity field on both the nearside and farside      
is important for operations in lunar orbit and to understand the internal       
composition and state of the Moon. Because global coverage is considered        
essential, two spacecraft are necessary to determine the gravity field (the     
nearside can be done with one); the second spacecraft is an extremely           
inexpensive "subsatellite" deployed directly from the main orbiter. The         
most rapid characterization of the global field would be achieved by a          
concept in which a passive laser reflector co-orbits with the main orbiter      
at a relatively low altitude. Instrument readiness will determine which         
technique is selected.                                                          

  Coupling imaging with altimetry and gravity will achieve excellent            
science return as well as operational information that would be of longterm     
use to the Exploration Initiative. The imaging system should be capable of      
taking stereo imaging data at a ground resolution of 15 m/pixel; a              
highresolution mode (2 m/pixel) would permit detailed study of specific         
sites for landed missions, either human or robotic. This global                 
cartographic database will serve exploration needs in both science and          
operations. Several imaging systems were considered: All would provide          
quality data and all have some flight hardware available.                       

Lander Mission  Surface Rover(s)                                                

Although landed payload instruments are not as highly developed, a capable      
suite of instruments can be available to fly on the prototype Artemis           
lander.                                                                         

  After considering several possibilities, the workshop concluded that a        
surface rover mission is a logical candidate for the first Artemis mission.     
JPL has been designing and fabricating test rovers for several years,           
including a set of minirovers, two of which could fit within the 65-kg          
payload of the first Artemis mission.                                           

  Several instruments could be mounted on such a rover to characterize in       
some detail the compositional and physical properties of a potential lunar      
outpost site. This mission could be either the prelude to more extensive        
surface investigation (by robotic or human missions) or a onetime               
exploration of a scientifically interesting or operationally challenging        
site.                                                                           

  An alpha-proton backscatter spectrometer would provide important              
information on the chemical composition of lunar soils. A Mossbauer             
backscatter spectrometer would complement the alphaproton instrument and        
provide highquality mineralogical data in addition to measurements of soil      
maturity. Stereo, highresolution cameras would document compositional           
analyses, permit physical characterization of the site, and allow all of us     
on Earth to share the excitement of the first return to the Moon.               

  These instruments are a minimum to return excellent scientific and            
resource characterization data. Other instruments, in particular an evolved     
gas analyzer to measure in situ concentrations of solar wind hydrogen,          
should be added to the rover payload as resources permit.                       

CONCLUSIONS                                                                     

Not only were logical collections of instruments identified to carry out        
specific exploration themes, but we found that it's highly probable that        
these instruments can be built, integrated onto a spacecraft bus, tested,       
and launched within the 3-year schedule proposed by the Office of               
Exploration. This is indeed a "faster, cheaper, better" way of  exploring       
space. Scientists who attended strongly endorse this new approach and stand     
ready to help the Office of Exploration carry out the Space Exploration         
Initiative.                                                                     

(Dr. Black is Director of LPI; Paul Spudis is a Staff Scientist                 
at LPI.)                                                                        

LEXSWG Orbital Dataset Requirements for Global Measurements                     

Priority     Measurement               Requirement                              
   1         Elemental Composition.....<100-km resolution                       
                                       <20% precision                           
   2         Topography................<1-km resolution                         
                                       <+10-m vertical                          
             Gravity...................<100-km resolution                       
                                       +1 mgal                                  
   3         Mineral Composition.......<500-m/pixel resolution                  
                                       +5% abundance                            
   4         Imaging...................15+5-m/pixel resolution                  
                                       100-300-m pos. accuracy                  
   5         Magnetic..................<30-km resolution                        
                                       +0.1-nT precision                        
   6         Atmosphere................Species present, state                   
                                       <100-km resolution                       
                                       +10% precision                           
   7         Surface thermal...........<100-km resolution                       
                                       0.5 degrees K (+4 mW/m^2)                
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