Beginning in late 1983, a team of engineers and scientists from NASA's Johnson Space Center (JSC), the Jet Propulsion Laboratory, and Science Applications Incorporated jointly defined a Mars Sample Return (MSR) spacecraft and mission plan (top link below). Among their proposed follow-on study objectives for Fiscal Year 1985 was to better define Mars sample quarantine protocols and associated risks. In addition, the team recognized the need to rapidly recover the Mars sample after its arrival at Earth. JSC's Solar System Exploration Division contracted with Houston-based Eagle Engineering to examine these issues and provide "rough" cost estimates. In its study, performed between May and September 1985, Eagle explored 10 options for retrieving a Mars sample following its return to Earth.
Eagle found that Direct Entry into Earth's atmosphere, with an estimated price tag of from $5.2 million to $9.8 million, would be the simplest and cheapest Mars sample recovery option, but would also carry the greatest risk (one chance in 600,000) of contaminating the terrestrial environment with potentially "malignant" martian microbes. Eagle acknowledged, however, that its contamination risk estimates (which, it explained, were based on "limited data") were arbitrary.
In Direct Entry, a reentry capsule carrying the sealed Mars sample canister would intersect Earth's atmosphere over the Pacific Ocean near Hawaii traveling at upwards of 11 kilometers per second. An ablative coating would protect the capsule from reentry heating. Eagle noted that a shallow atmosphere-entry angle would subject the sample canister to a long heat pulse, a low deceleration load, and imprecise landing site targeting (and, therefore, possible delayed recovery), while a steep angle would yield a short heat pulse, a high deceleration load, and more precise targeting.
After slowing to subsonic speed, the capsule would deploy a 5.5-meter-diameter parachute. A Defense Department transport aircraft - probably a C-130 - would snatch the descending capsule by the parachute in midair and winch it into its cargo hold, then would fly directly to the Centers for Disease Control (CDC) in Atlanta, Georgia, or to a newly constructed Planetary Sample Receiving Laboratory (PSRL) in a remote location. Eagle did not include the $14-million cost of the new lab in its cost estimates. The company assumed that the C-130 would be one of three similarly configured air-snatch planes in the recovery area, each of which would carry 11 aircrew on board.
Eagle's second option was Shuttle Recovery, which, the company estimated, would have only one chance in 100 million of releasing potentially harmful martian microbes into the terrestrial environment. A delta-winged Space Shuttle Orbiter would be prepositioned in Earth orbit in anticipation of the arrival of an Earth Return Vehicle (ERV) bearing the sample canister. The ERV would skim through Earth's upper atmosphere to use drag to slow down (that is, it would aerobrake) and enter an elliptical Earth orbit. It would then discard its protective aeroshell and fire a rocket motor at the apoapsis (high point) of its orbit to raise the periapsis (low point) of its orbit above the atmosphere and circularize its path around the Earth.
Eagle noted that the Shuttle Orbiter was incapable of climbing higher than about 500 kilometers above the Earth (in fact, it reached about 610 kilometers during STS-31, the Hubble Space Telescope deployment mission, in April 1990). If the ERV's orbit following the apoapsis burn was above the Shuttle altitude limit, then the Orbiter would need to deploy a teleoperated Orbital Maneuvering Vehicle (OMV). The OMV would match orbits with the ERV, dock with it, lower its orbit, and then separate.
After the Shuttle Orbiter rendezvoused with the ERV, the astronauts would capture it using their spacecraft's robot arm and place it inside a seven-ton biological containment/sample cooling container in the Orbiter's payload bay for return to Earth. The container would, Eagle wrote, be designed to survive intact a Shuttle accident during reentry and landing. A slightly cheaper but "significantly" more risk-fraught alternative would be for a spacewalking astronaut to extract the sample canister from the ERV and carry it into the two-deck Orbiter crew cabin for return to Earth.
Eagle placed the cost of the Shuttle return option at between $150 million and $173 million, of which $120 million would, in theory, pay for the Space Shuttle flight (in practice, Space Shuttle flights were considerable more expensive than this). The company also examined recovery of the sample from a high elliptical Earth orbit (the 1984 JSC/JPL/SAI design study proposed that the ERV capture into such an orbit). Eagle found that the Orbital Transfer Vehicle (OTV) required to reach such an orbit would boost their estimated cost by from $50 million to $100 million.
Eagle's third recovery option was Recovery to Space Station Structure. The company estimated that for this and all subsequent recovery options, the likelihood that harmful martian microbes could escape into Earth's environment would be less than one chance in 100 million. A Shuttle Orbiter would deliver to NASA's Space Station in 500-kilometer-high Earth orbit a biological containment/sample cooling container and three tons of propellants for a Station-based OMV. This would, the company noted, make use of about half the Shuttle's payload capacity, leaving the other half for additional Station-bound cargo unrelated to the sample recovery operation.
Spacewalking astronauts would attach the containment/cooling container to the Station's exterior. Some time after that, the ERV would aerobrake and maneuver into a circular orbit. The Station crew would then dispatch an OMV to recover it and bring it to the Station.
The Station's robot arm would transfer the ERV from the OMV to the containment/cooling container. A Shuttle mission to the Station would then collect the container for return to Earth, along with about half a payload bay of Earth-bound cargo unrelated to the sample recovery operation. Eagle placed the cost of this option at between $167 million and $193 million.
Option 4, Space Station Sample Repackaging, would see a Shuttle Orbiter deliver parts for modifying the Life Sciences Module (LSM) airlock that was expected to be part of the Space Station along with propellants for a Station-based OMV. Alternately, a Shuttle mission would detach the LSM from the Station and transport it to Earth for modification, after which a second Shuttle mission would return it to the Station.
The OMV would capture the ERV and deliver it to the LSM airlock, where astronauts would extract the sample canister and repackage it within a small biological containment/sample cooling container. The container would then be returned to Earth inside a Shuttle Orbiter crew cabin. The ERV would remain in quarantine inside the LSM airlock until scientists in the PRSL on Earth had analyzed the returned Mars sample and determined that it posed no threat. Eagle estimated that this option would cost between $302 million and $714 million.
Option 5, for which Eagle had little enthusiasm, was dubbed Minimal Sample Analysis at Space Station. It would closely resemble Option 4, except that a small sub-sample would removed from the sample canister in the LSM for "minimal" biological analysis. "There is some question," the company noted, "as to how much use a minimal analysis would be." Eagle placed the cost of this option at between $316 million and $749 million.
Eagle's Option 6, Small Sample Sterilized at Station and Sent to Earth, was also derived from its Option 4. Astronauts would remove a sub-sample and heat it enough to kill martian microbes while preserving evidence of their existence. A Shuttle Orbiter would then transport the sub-sample to Earth. The remainder of the sample (and, possibly, the Station crew) would remain in quarantine until scientists in the PSRL had checked out the sub-sample. Eagle placed this option's cost at between $316 million and $927 million.
After Option 6, Eagle's proposed sample-handling options became much more complex and expensive, adding significantly to the cost of returning a sample from Mars. Option 7, Separate Quarantine Module Attached to Station, would see a Shuttle Orbiter dock a specialized LSM-derived Quarantine Module (QM) to the Station. Eagle noted that the cost of "[d]edicated facilities. . .will seem more reasonable if a number of sample return missions are envisioned," and added that "[m]anned Mars missions might. . .use the [QM]" for quarantine of astronauts returning from Mars.
No pressurized passageway would link the Station to the QM while it held a Mars sample. If the QM was a permanent module of the Space Station, then it might be connected to it by a pressurized tunnel when no Mars sample was present and put to non-sample-related uses.
Alternately, the QM might be attached to the Station only when a sample was due to arrive from Mars. After the sample was placed in the QM, a Shuttle Orbiter would detach the module and transport it to Earth. Another Orbiter would return the empty QM to the Station when the next Mars sample was due to arrive in Earth orbit. Eagle estimated that Option 7 would cost between $605 million and $1.04 billion.
Antaeus Lab Module Attached to Station, Eagle's Option 8, took its name from the 1981 Antaeus report (bottom link below), which described a purpose-built Orbital Quarantine Facility (OQF) space station. The Antaeus module, which would be capable of supporting long-term detailed sample analysis on much the same scale as the Earth-based PRSL, would replace or augment the Station's LSM.
If researchers working in the Antaeus module found that the Mars sample was safe, then it would be transported to Earth. If, on the other hand, the sample were found to contain harmful martian microbes, then the Antaeus module would be detached and boosted into a 1270-kilometer-high long-term orbit using an OMV. In the event that harmful microbes escaped from the Antaeus module and contaminated the Space Station, then an OMV could boost the entire Station into a 650-kilometer-high orbit. Eagle estimated that orbit-raising maneuvers could extend the orbital lifetime of the Antaeus module or Station for long enough to permit NASA to develop a large rocket stage that could boost the contaminated Antaeus module or Station into interplanetary space.
Augmenting the Space Station with the Antaeus module would require perhaps eight Shuttle flights at an estimated cost of $120 million each, for a total of $960 million. The company placed the total cost of Option 8 at between $1.863 billion and $2.456 billion.
Eagle's Option 9, the 1/2 Quarantined Space Station, would be nearly identical to its Option 8, except that the Station modules that would support the scientists analyzing the sample in the Antaeus module would be isolated from the rest of the Station. This would be achieved by closing pressure hatches between the two halves of the Station and slightly reducing air pressure in the quarantined modules. Eagle expected that this option would cost the same as Option 8, though it added that "detailed study may show this option to have a somewhat higher cost."
Option 10, a Dedicated Antaeus Space Station identical to that described in the Antaeus report, would constitute a new (albeit small) independent space station in Earth orbit, making it the costliest of the 10 options. Eagle estimated that the Antaeus station would cost between $5.101 billion and $7.107 billion. This option would make unnecessary the PSRL on Earth since all quarantine and analysis would take place in Earth orbit. The company declared that Option 10 was "without a doubt the safest, biologically, of all the options," but added that "the price paid for this additional safety seems unreasonably high."
Having examined the 10 options, each more complex than the last, Eagle judged that Options 1, 2, and 3 would be adequate for Mars sample quarantine. The probability of a biological accident involving a Mars sample was simply too minute to justify the greater cost of Options 4 through 10.
The company then examined methods of Earth-orbital sample recovery. It assumed that, during Mars-Earth transfer, the sample would be preserved at cold Mars-like temperatures to maintain its scientific integrity. Earth orbit is, however, warmer than interplanetary space because Earth radiates heat. This would make difficult keeping the Mars sample cold for long periods in Earth orbit, so rapid recovery would be desirable.
Eagle also assumed that an ERV that employed rocket motors to slow itself so that Earth's gravity could capture it would end up in a high elliptical Earth orbit (700 kilometers by 40,000 kilometers or 700 kilometers by 70,000 kilometers, with orbital periods of 12 or 24 hours, respectively). This would have the advantage of placing it well away from the Earth's radiated heat through most of its orbit, but would also delay sample recovery.
For recovery from elliptical orbit, the planned OMV design would be inadequate, so Eagle invoked a new-design Orbital Transfer Vehicle (OTV) based on the Centaur upper stage. Recovery using an OTV based at the Station would be problematic because the Station's orbital plane would shift 6° per day relative to the ERV, forcing the OTV to burn a considerable quantity of propellant to match orbits with the ERV and return with it to the Station. Eagle found that the best-case recovery time for a sample in elliptical orbit would be equal to one orbital period (12 or 24 hours) plus about four hours, leading to totals of 16 or 28 hours.
A sample in a 500-kilometer circular orbit, on the other hand, would be subjected to more Earth-radiated heat, but could be recovered by a Shuttle Orbiter or an Orbiter- or Station-based OMV in as little as six hours. Providing the ERV with enough propellant to circularize its orbit at 500-kilometer altitude would, however, increase its mass by 2.5 times over the elliptical-orbit ERV. This would constitute "an unacceptable penalty," Eagle judged.
Planetary Sample Rapid Recovery and Handling, Report No. 85-105, Eagle Engineering, September 20, 1985.
http://beyondapollo.blogspot.com/2010/09/jpljsc-mars-sample-return-study-i-1984.html
http://beyondapollo.blogspot.com/2009/09/antaeus-report-1978.html
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