When the Stardust capsule blazed its way through Earth’s atmosphere to a parachute landing in Utah earlier this month, the event was a preview of extraterrestrial attractions to come.
Scientists are elated at the Stardust collectibles — pristine specimens of interstellar dust and comet particles from deep space.
Attention is now turning toward other objects: the moon, Mars, comets and asteroids, even Venus and Saturn’s Titan. All are appetizing targets in the celestial sweet shop of cosmic sampling.
Following nearly seven years of travel, the Stardust sample return capsule became a long-distance, express mail, record-setting delivery. It achieved the highest return velocity — 29,000 miles per hour (12.8 kilometers a second) of any human-made Earth re-entry object to date.
“The capsule showed excellent performance,” said Jim Crocker, vice president of civil space at Lockheed Martin Space Systems of Denver. The company designed, built and operated Stardust.
“There was no evidence of heat shield distress or any unexpected grooving or pitting. When the capsule was opened, it was pristine inside. There was no evidence of any leaking or heating trauma. It all looks cleanroom-fresh on the inside. That’s extremely good news,” Crocker told Space.com.
Space engineers are keen to do detailed engineering measurements on how much the capsule ablated during its fiery plunge to Earth on Jan. 15. An essential element of the capsule was its heat shield, resembling a blunt-nosed cone that thwarted the blistering temperatures reached during Earth re-entry.
Right on target
The heat shield on Stardust’s sample return capsule consisted of two parts: a lightweight aeroshell structure and a thermal protection system, or TPS. The TPS is a flight-qualified version of the high-energy ablator PICA — Phenolic Impregnated Carbon Ablator — invented by NASA Ames Research Center. Stardust represented the first flight of this material.
The backshell TPS is the same material used for the heat shields with the Mars Pathfinder mission and the Mars Exploration Rover missions — Spirit and Opportunity — and was first developed by Lockheed Martin for use on the Viking missions to Mars in the 1970s.
In September 2004, the Genesis spacecraft — also built by Lockheed Martin for NASA — delivered its return capsule right on target into Utah. But due to improper placement of onboard components that would activate the capsule’s parachute recovery system, that hardware plowed into desert landscape at high speed. Despite this ballistic blemish of an ending, scientists have apparently recovered meaningful science from Genesis-snared solar wind samples.
Crocker said that the analyses of the Stardust and Genesis capsules — as well as the Opportunity rover's surveying of its own heat shield that plummeted onto Mars — all yield data extremely useful in designing future sample return hardware.
“Every kilogram of material that you put on a heat shield that’s in excess of what you need for a reasonable margin … that’s a kilogram of payload that you can’t put down on the planet,” Crocker said. “By reducing the uncertainty of how these things perform, it greatly improves our performance of the whole mission.”
“Stardust is really a trailblazer for an inexpensive way of returning extraterrestrial materials to Earth … and it worked wonderfully,” said Laurie Leshin, Director of Sciences and Exploration at NASA’s Goddard Space Flight Center in Greenbelt, Md.
Leshin said she and other scientists are anxious to dive into Stardust’s captured comet grains and study them in detail. She is a member of the Preliminary Examination Team that will get an early look-see at the samples.
“I predict that we will be blown away by the discoveries we will make in the next few months,” Leshin told Space.com. “We simply can’t fly in space the equivalent of the thousands of tons of sophisticated lab equipment we have here on Earth. So if we can’t bring the instruments to the comet, we’ve got to bring the comet to the instruments.”
‘SCIMing’ off the top
Thanks to Stardust’s success, Leshin said, it’s time to ask whether the same approach can be utilized to bring precious samples from other objects back to Earth.
One such concept for a Stardust-style mission is tagged SCIM — short for Sample Collection for Investigation of Mars. This proposed spacecraft would “skim” through the Martian atmosphere, sweeping up dust and gas samples for analysis back here on Earth, Leshin explained.
“Scientists have been calling for sample return missions from Mars for over 30 years, but they have always proven too technically challenging and expensive to undertake,” Leshin said. “With a mission like SCIM, we can get Martian dirt back to Earth for about one-tenth the cost of a more traditional sample return mission, and for about half the cost of the Mars rovers!”
Leshin is part of a team currently working on a proposal to NASA to fly SCIM in 2011.
Quantum step forward
“Stardust is a huge success of a mission,” said Stephen Mackwell, director of the Lunar and Planetary Institute in Houston. “In the coming months, as the samples are analyzed, I anticipate a quantum step forward in our understanding of comets … bodies that still contain material from the earliest evolutionary stages of the solar system,” he said.
Material snatched from space by Stardust will be available to scientists from around the world. Researchers can study the samples using a broad array of conventional and innovative techniques.
“It really does give great support to the concept of grabbing materials for analysis here on Earth. You can do so much more here than using instruments on a remote vehicle,” Mackwell noted.
For instance, take the work of the Spirit and Opportunity Mars rovers.
Mackwell offered one hypothetical: “Just think what more we could have done with a scoop of Mars dirt, including a few blueberries, or a chunk of sedimentary layering, with a full chemical analysis and age dating, etc., back here on Earth,” he said. The rovers have highlighted so many new questions that can be answered for the most part only by returned samples, he said.
Some level of paranoia
The question of sample return is much debated in the planetary sciences community, Mackwell advised.
“Because sample return involves two-way travel, potentially including second liftoff from a body with significant gravity — Mars or Venus, for example — and issues of planetary protection…these missions are almost always expensive relative to orbital missions, or even landed missions with or without rovers,” Mackwell said.
Added to the technical difficulty and cost, Mackwell continued, are societal issues with returning samples from planetary bodies that may have once sustained some form of life.
“Even the remote chance that such lifeforms might be capable of biological interaction with Earth organisms induces some level of paranoia, justified or not,” Mackwell said. “For these reasons, sample return missions from Mars have remained just at the edge of the future planning cycle for decades and have only recently been pushed even further out. Return missions from comets, asteroids and other small lifeless bodies are still technically challenging, but cheaper and less likely to invoke fear,” he suggested.
Dig and dash
NASA is not alone in bringing back the goods from space via automated capsules.
The former Soviet Union used the robotic dig-and-dash technique to fly back to Earth lunar specimens.
Then there’s Japan’s valiant Hayabusa probe. Late last year it reached out and touched an asteroid. That craft suffered hardware problems and is now limping back to Earth for a 2010 capsule landing. Scientists still hold onto hope that Hayabusa may well have tucked away bits and pieces of asteroid.
The Lunar and Planetary Institute’s Mackwell spotlighted the value of sample return missions to other planetary bodies — notably Titan, with its exotic surface; and Venus, so much like Earth and yet so different.
“Such missions would greatly advance our knowledge of our solar system and evolution of the interiors and surfaces of the planetary bodies and the diversity of environments that exist within our corner of the universe,” Mackwell said.
The gift that keeps on giving
The inevitable question is ascribing value of sample return to Earth contrasted to one-way landers, surface rovers and other mobile hardware. And these tactics can be compared to what instrument-laden orbiters bring to the table.
The difficulty here, Mackwell said, is just how much instrumentation can fit on outward-bound spacecraft. Not only are there power and mass issues, but what size sample can be assessed and in what state.
“Samples are pieces of the surface and can provide ground truth for remotely sensed data, allowing calibration of orbital or balloon measurements. Thus, they make remotely sensed data far more valuable. In addition, data derived from samples provide a unique perspective not offered by either orbital or in-situ [on-the-spot] data,” Mackwell said.
Samples brought back to Earth “are the gift that keeps on giving,” Mackwell said, given analytical experiments on samples that can be modified “as logic and technology dictates.”
And finally, returned samples, properly handled, permit scientists to assess any biological hazard on another planet prior to sending humans, Mackwell concluded. “Given the huge potential return in science from samples returned to the Earth for analysis, the additional cost of these missions is easily justified.”