Giotto II (1985)

On the overcast morning of July 2, 1985, the eleventh Ariane 1 rocket launch took place at the Centre Spatial Guyanais in Kourou, French Guiana, an outpost of the European Community located a few degrees north of the equator on the northeast coast of South America (top image above). The last Ariane 1 to fly, it bore aloft Giotto, the first European Space Agency (ESA) interplanetary spacecraft (middle image above). Giotto's destination was Comet Halley.

A "dirty snowball" containing materials left over from the birth of the Solar System 4.6 billion years ago, Halley needs about 76 years to revolve around the Sun once. Its elongated orbit takes it as near to the Sun as the space between the orbits of Venus and Mercury and as far from the Sun as the cold emptiness beyond the orbit of Uranus.

Comet Halley has passed through the inner Solar System 42 times since its first recorded apparition. In 837, it passed just 5.1 million kilometers from Earth; during that apparition, its dust tail must have spanned nearly half the sky, and its bright coma - the roughly spherical dust and gas cloud surrounding its icy nucleus - may have been as large as the full moon. During its apparition of 1301, Italian artist Giotto di Bondone painted Comet Halley. The Giotto spacecraft was named for him.

The Ariane 1's third stage injected 980-kilogram Giotto into a 198.5-by-36,000-kilometer orbit about the Earth. Thirty-two hours after launch, as it completed its third orbit, flight controllers in Darmstadt in the Federal Republic of Germany commanded Giotto to ignite its French-built Mage solid-propellant rocket motor. The aft-pointing motor burned 374 kilograms of propellant in 55 seconds to inject the spinning 2.85-meter-tall, 1.85-meter-diameter spacecraft into orbit about the Sun.

Two months before Giotto's launch, Americans P. Tsou (Jet Propulsion Laboratory), D. Brownlee (University of Washington), and A. Albee (Caltech) proposed in a paper in the Journal of the British Interplanetary Society that a second Giotto mission be dispatched to fly close by one of 13 candidate comets between 1988 and 1994. The spacecraft, which they dubbed Giotto II, might launch on an Ariane 3 or in the payload bay of a Space Shuttle. Giotto II's "free-return" trajectory would take it as close as 80 kilometers from the target comet's nucleus, then would return it to Earth. Near the comet, Giotto II would expose sample collectors to the dusty cometary environment. Near Earth, it would eject a sample-return capsule based on the proven General Electric (GE) Satellite Recovery Vehicle (SRV) design. The capsule would enter Earth's atmosphere to deliver its precious cargo of comet dust to eager scientists.

Tsou, Brownlee, and Albee pointed out that the Mage solid-propellant motor was not required to boost Giotto into interplanetary space; that is, that the Ariane 1 could do the job itself. Giotto was, however, based on a British Aerospace-built Geos magnetospheric satellite design, which included the Mage motor. Re-testing the design without the motor would have cost time and money, so ESA elected to retain it for Giotto. After noting that the GE SRV could fit comfortably in the space reserved for the Mage, they proposed that the reentry capsule replace the motor in Giotto II.

Giotto included a "whipple bumper" on its aft end to protect it from hypervelocity dust impacts. During approach to Comet Halley, the spacecraft would turn the bumper in its direction of flight. The bumper comprised a one-millimeter-thick aluminum shield plate designed to break up, vaporize, and slow impactors, a 25-centimeter empty space, and a 12-millimeter-thick Kevlar sheet to halt the partially vaporized, partially fragmented impactors that penetrated the aluminum shield.

In the case of Comet Halley, dust would impact the bumper at up to 68 kilometers per second. Tsou, Brownlee, and Albee noted that the 13 candidate Giotto II comets were all less dusty and would have lower dust impact velocities than Halley. Because of this, Giotto II would need less shielding than Giotto.

Impacting dust would nonetheless create challenges for Giotto II. Tsou, Brownlee, and Albee devoted much attention in their paper to how the spacecraft might successfully capture dust for return to Earth. One capture system, a variant of the whipple bumper, would use a shield made from ultrapure material to vaporize and slow impacting dust particles. The vapor from the impactor and the impacted part of the bumper would then be captured as it condensed. Scientists would disregard the bumper material when they analyzed the condensate.

Tsou, Brownlee, and Albee then noted that thermal blankets returned from the Earth-orbiting Solar Maximum Mission satellite had shown that intact capture of high-velocity particles was possible. The multilayer Kapton/Mylar blankets collected hundreds of intact meteoroids and human-made orbital debris particles. They described preliminary experiments in which "underdense materials" (polymer foams and fiber felts) were subjected to high-velocity impacts by meteoroid and glass fragments fired from gas guns. The experiments suggested that such materials could indeed capture at least partially intact dust particles.

Giotto flew past the Comet Halley nucleus (top image below) at a distance of 596 kilometers on March 13-14, 1986. The comet's 15-by-eight-kilometer heart was extremely dark, with powerful jets of dust and gas blasting into space.

The intrepid probe suffered damage from dust impacts - for example, one large particle sheered off more than half a kilogram of its structure - but most of its instruments continued to operate. ESA thus decided to steer it toward another comet. On July 2, 1990, five years to the day after its launch, Giotto flew past Earth at a distance of 16,300 kilometers, becoming the first interplanetary spacecraft to receive a gravity-assist boost from its homeworld. The gravity assist put it on course for Comet Grigg-Skjellurup, which it flew past at a distance of 200 kilometers on July 10, 1992. After determining that Giotto had less than seven kilograms of hydrazine propellant left on board, ESA turned it off on July 23, 1992. The inert spacecraft flew past Earth a second time at a distance of 219,000 kilometers on July 1, 1999.

By that time, a comet coma sample return mission was under way with two of the Giotto II proposers playing central roles. In late 1995, Stardust became the fourth mission selected for NASA's Discovery Program. Brownlee was Stardust Principal Investigator and Tsou, Stardust Deputy Principal Investigator, designed the mission's sample capture system. The 380-kilogram Stardust spacecraft (top image below) left Earth on a free-return trajectory on February 7, 1999 and flew past Comet Wild 2 (one of the 13 Giotto II candidates) at a distance of about 200 kilometers on January 2, 2004. Stardust captured dust particles in aerogel, a silica-based material of extremely low density that was not available when Tsou, Brownlee, and Albee proposed Giotto II.

Stardust returned to Earth on January 15, 2006. Its sample capsule streaked through the pre-dawn sky over the U.S. West Coast before parachuting to a landing on a salt pan in Utah (bottom image below). When opened on January 17, 2006 at NASA's Johnson Space Center, Stardust's 132 aerogel capture cells contained thousands of intact dust grains captured from Wild 2. Subsequent analysis indicated that some probably formed close to other stars before the Solar System was born.

"Comet Coma Sample Return via Giotto II," P. Tsou, D. Brownlee, and A. Albee, Journal of the British Interplanetary Society, Volume 38, May 1985, pp. 232-239.

Mars Sample Return quarantine & recovery (1985)

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.

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