Good Things Delivered in Small Packages

NASA recently asked industry for concepts of small robotic landers for missions to the Moon. What could such machines accomplish?

Prototype small lunar landers developed by NASA undergo testing. At left, Marshall's Mighty Eagle; at right, JSC's Morpheus.

Wanted: lander spacecraft to deliver payloads to the Moon.  Must be cheap and reliable.

NASA recently issued an “RFI” – a Request for Information – a method used by the agency to solicit concepts from various companies and gauge their ability to fulfill a future anticipated need.  In this case, the need is for a small robotic lander, one capable of delivering two classes of payloads to the lunar surface: small (from 30 to 100 kg) and medium (from 250 to 450 kg).

Probably focused near-term with the RESOLVE (Regolith and Environment Science and Oxygen and Lunar Volatiles Extraction) payload, the intent of this RFI is to survey existing capabilities for the commercial delivery of a variety of payloads to the Moon.  RESOLVE is a NASA experiment designed to test and demonstrate some techniques of in situ resource utilization (ISRU) on the Moon, specifically the generation of oxygen and the extraction of volatile elements (such as hydrogen) from lunar soil.  The RESOLVE package consists of several highly integrated experiments designed to collect soil on the Moon, heat this feedstock to various temperatures and measure the amount and type of volatile elements released, and practice some techniques of processing the soil into useful products (such as water or oxygen).

Though we’ve been talking about using off-planet resources for years, this is the first time the agency would fly an experiment designed to evaluate the processes and difficulties involved.  Some of us contend that until it is proven possible (by demonstrating it in space), space-based resource utilization (ISRU) will remain classified as “too risky” to incorporate into an architecture.  Engineers don’t doubt the chemistry or physics behind ISRU, but to evaluate risk and return, they want demonstrations using real hardware versus theoretical concepts and paper studies.

Although it will not answer all ISRU questions, RESOVLE can provide useful data and would be an important milestone.  Our ignorance is particularly vast in regard to the nature of the polar volatile deposits.  Some near-polar sites are under consideration for RESOLVE, but because the lander must be able to communicate with Earth, sites near the poles must be in radio view of Earth.  This eliminates the most promising polar volatile sites (permanently dark, out of radio sight) from consideration, at least for the first mission.  However, we know that water ice occurs in some areas in view of Earth, so careful targeting will permit us to get ground truth for a critical area near the one of poles.

There are a wide variety of possible payloads (scientific and resource utilization) for lunar missions using small landers.  A key priority for the lunar science community has been the deployment of a global network of geophysical instruments.  Such a package would include a seismometer (to monitor and measure moonquakes), a heat flow probe (to take the Moon’s temperature) and other instruments, such as a magnetometer and a laser reflector.  The five-station surface network laid out during the Apollo missions was operational for more than 7 years and gave us a first-order understanding of the nature of the deep lunar interior.  A new global network – widely spaced and operating longer with more stations – would vastly improve on that knowledge.

The success of a network mission necessitates a long-lived power source to operate instruments during the very cold, 14-day lunar night (the Apollo network used nuclear power supplies), along with an inexpensive way to deploy the network stations.  New technologies have developed small, reliable radioisotope generators that operate for many years.  A small lander could deliver geophysical stations across the entire globe; each station is low mass, so the smaller (and presumably cheaper) the lander, the more likely that this mission will be realized.  A global seismic network would decipher the crust and mantle structure of the Moon and could monitor its surface for large impacts.  A precise measurement of lunar heat flow (measuring the abundance of radioactive elements in the Moon) will give us more information about the bulk composition of the Moon and advance our understanding of lunar origin.  Laser ranging will also be useful in addressing some critical geophysical and astrophysical problems.

Single-point landers, making simple measurements, can investigate the surface composition and geology at select landing sites.  If the landing sites and investigations are carefully chosen, they could significantly advance science by answering key questions.  For example, a critical issue in the cratering history of the Moon is knowledge of the absolute age of some of the youngest craters on the Moon.  The formation of the crater Copernicus marks a key time horizon in lunar history (the Copernican Period).  We know its relative age very well but are uncertain about its absolute age.  A small lander can be sent directly to the crater floor, where the impact melt is exposed and accessible, to analyze crater melt rocks for chemical composition and to learn the nature of the impact target (as well as determining the age of the rock by measuring the radiogenic potassium and argon in the rock). Although the potassium-argon technique is not the most precise method of radiometric dating, it can distinguish among the different proposed absolute ages, which vary over a billion years.  By determining this age more precisely, we will better understand the impact flux in the Earth-Moon system, knowledge that will help us better interpret the surface ages of units on other terrestrial planets.

Small landers could deliver a variety of long-lived assets for future surface operations and resource utilization experiments.  Techniques for making oxygen from lunar soil have been proposed but no comparative demonstration has been done on the Moon.  A small laboratory could be send to the Moon to conduct simultaneous experiments on oxygen manufacture.  The advantage of this experiment would be the use of identical feedstock under identical thermal and time constraints to compare their relative efficacy and identify any problems.  This experiment would fit on a small lander (~ 50 kg capacity) and by using solar power, within the span of a single lunar day (2 weeks) could quickly complete its evaluation.

The larger version of the RFI lander opens up other possibilities.  With a payload capacity on the order of 500 kg, this lander could deliver an advanced, automated surface rover (powered by an RTG – nuclear battery) able to undertake extensive and protracted exploration of the polar cold traps.  Equipped with instruments utilizing well established technology, this rover would characterize the physical, chemical and isotopic make up of the polar volatiles – a task critical for mapping the extent and purity of deposits of water ice on the Moon, and evaluating their mining and extraction potential.

At this scale, it’s possible to deliver an ascent vehicle to the Moon to retrieve and return samples to Earth.  Scientists have a long list of desired targets for sample return and the potential for low cost, commercial landers to deliver payloads simply and inexpensively to the Moon could revolutionize our understanding of the Moon’s (and Earth’s) history and processes.  From remote sensing data, we know that many fascinating areas on the Moon display rocks either unrepresented or unrecognized in the existing collections from the American Apollo, Soviet Luna, and lunar meteorite samples.  Samples from the oldest impact feature on the Moon – the floor of the South Pole-Aitken basin – are especially desired.  Although a simple “grab” sample won’t answer all of our questions, rocks from this site could address major questions about the bombardment history of the Moon and the early Earth.

Small lander spacecraft will open up new horizons for science and exploration.  Critical to their success is making them simple, robust and inexpensive.  That’s been a tall order for NASA.  Whether the commercial sector can provide this capability more effectively remains to be seen.

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