A bridge to Venus
by Jeff Foust
|“I think many of you share my feeling that NASA passed by an opportunity to take a new direction and reengage in some fundamental questions of comparative planetology that Venus uniquely provides,” said Grimm.|
Among those watching anxiously for the New Frontiers announcement will be those planetary scientists who study Venus. A year ago they had high hopes for winning approval for NASA’s first mission to the planet since Magellan, more than a quarter-century ago. Two of the five finalists in the competition for the Discovery program of less-expensive planetary spacecraft were Venus missions. With NASA planning to select two missions at once, the odds were good that one of them would be a Venus mission.
The odds, alas, were not good enough. NASA instead picked two missions to study asteroids, Lucy and Psyche, while also providing funding for an asteroid-hunting space telescope, NEOCam, to allow for additional mission studies. The two Venus missions in the competition, DAVINCI and VERITAS (see “For planetary scientists, Venus is hot again”, The Space Review, December 12, 2016), were left out.
“I think many of you share my feeling that NASA passed by an opportunity to take a new direction and reengage in some fundamental questions of comparative planetology that Venus uniquely provides,” said Robert Grimm, a Southwest Research Institute planetary scientist who chairs the Venus Exploration and Analysis Group (VEXAG), at the group’s annual meeting last month at the Applied Physics Laboratory.
Grimm said the leadership of VEXAG met with Thomas Zurbuchen, the associate administrator for science at NASA, for a debrief after the Discovery mission announcements early this year. “He assured us there was no bias against Venus in the selection,” he said. “The Venus community, I think, has rebounded.”
Part of that rebound has to do with the New Frontiers competition: three of the mission proposals submitted involve orbiter or lander missions to Venus. However, Grimm said at the meeting that Zurbuchen opened the door to another type of mission, far smaller than a New Frontiers or Discovery mission.
“During that debriefing, Dr. Zurbuchen posed a question to us: what could you do for $200 million?” Grimm recalled. “We thought maybe a couple of smallsats.”
NASA, earlier this year, awarded a number of studies for its Planetary Science Deep Space SmallSat (PSDS3) program. These studies are intended to explore the feasibility of using smallsats, from 180 kilograms down to CubeSats, for various planetary science missions. The awards included four concepts for missions to Venus.
|“We think that there’s strong science that can be done,” Grimm said of smallsat missions. “The $200 million cap can be met with programmatic considerations.”|
Grimm said that VEXAG wanted the opportunity to do more than just support studies of individual PSDS3 missions. Could there be a way to combine such missions? “The possibility of a directed effort at this $200 million cap lets us study linked missions to Venus,” he said. “By sending, say, an orbiter and a lander or a balloon or an atmospheric probe, that are part of a linked package, the whole can be bigger than the sum of its parts.”
That led to an ongoing study called Venus Bridge to look at the feasibility of linked smallsat missions to Venus, including their ability to perform useful science and fit within that $200 million cost cap. The studies, briefed at the VEXAG meeting, are still ongoing, but those involved sounded optimistic about their outcome.
“We think that there’s strong science that can be done,” Grimm said. “The $200 million cap can be met with programmatic considerations.” Those “programmatic considerations,” he said, included whether you include launch and operations cost within the cap or treat them separately, as is often the case with other missions.
Two separate Venus Bridge studies are in progress, one at JPL and the other at the Glenn Research Center. Jim Cutts of JPL, briefing VEXAG on one of the studies, dubbed “Team X,” took a cautionary note compared to Grimm. “Bob’s statements about thinking a $200 million program is feasible is not something I’m prepared to buy into yet,” he said. “I think it’s possible, but I don’t think it can be proven yet.”
One of the biggest challenges is how to get a smallsat mission to Venus. “A dedicated launch vehicle isn’t affordable,” Cutts said. Instead, he said, such a mission would have to fly as a secondary payload as part of a larger mission to Venus, a lunar mission, or a spacecraft flying to geostationary transfer orbit (GTO). A GTO rideshare is attractive, he said, given the large number of launch opportunities. But, he said, “reaching Venus orbit directly from GTO is something of a stretch.”
Results were encouraging on aspects of the spacecraft themselves. Cutts noted the Pioneer Venus mission of the late 1970s included atmospheric probes, each weighing 63 kilograms, that survived to the surface of Venus. “How small can we go?” he asked. “We think we can probes down to three kilograms and still survive.”
A balloon mission, he said, may be harder, since is appears difficult to fit one into an aeroshell 56 centimeters across, a size constraint for flying as a rideshare mission.
The other study, called Venus Bridge Orbiter and Surface System (V-BOSS), is examining a specific design for a coupled orbiter and lander mission to see if the overall concept is feasible, said Gary Hunter of NASA Glenn. “In order to know if we could make $200 million, we had to go through a point design,” he said, adding there are various options that can also be considered for such a mission.
|“Can you do it?” Hunter asked. “From this study, we’re suggesting that there is a way to provide science and we’re within or close to $200 million, with some assumptions.”|
The V-BOSS concept his team is looking at involves an orbiter and a lander to study mineralogy and surface-atmosphere interactions. It takes advantage of high-temperature electronics being developed and tested at Glenn to allow for the lander to operate for an extended period on the surface.
In this mission, V-BOSS would launch as a secondary payload on a mission towards the Moon in 2025, and make flybys of both the Moon and Earth en route to Venus. The lander, weighing about seven kilograms, would separate from the orbiter about 30 days before arrival. The lander would collect data during descent and after landing, transmitting it to the orbiter to relay to Earth. The orbiter, in addition to being a communications relay, would take infrared images of the Venus.
The orbiter and lander observations will be coupled, allowing for comparisons between the two, Hunter emphasized. The lander will land at night, he said, to support those coupled infrared observations for “a significant period of time.”
With that point design in place, the study team made an estimate of the mission’s cost. A key point, he said, was not limiting the orbiter and lander to individual cost caps of $100 million each, which would have been the case if they were developed as independent PSDS3 missions. “If it was $100 million and $100 million, that was going to be a problem,” he said. “Call it $140 million or so for the orbiter, and $60 million for something akin to the lander.”
The cost model presented at the VEXAG meeting has an overall estimate for V-BOSS of $202 million, which includes reserves of 25 percent. It does not, he said, include launch and operations costs.
“Can you do it?” he asked. “From this study, we’re suggesting that there is a way to provide science and we’re within or close to $200 million, with some assumptions.”
The two studies will continue into early next year. What happens after that, particularly if the studies do conclude that such missions can do useful science within the $200 million cost cap, isn’t clear. Grimm said he believes that Zurbuchen, who was an advocate of the use of cubesats for science missions before joining NASA last year, is sincerely interested in finding a way to back a smallsat Venus mission program.
“When the AA asked us this question,” Grimm said of that meeting with Zurbuchen when he proposed a $200-million Venus mission, “we thought it was sort of spontaneous. I’ve since thought that, maybe, this is what he wanted to ask us.”
The Venus Bridge studies do provide new optimism for scientists after the loss of the Discovery competition. At the very least, the future of NASA-funded missions to Venus is not riding on the outcome of the New Frontiers competition, where Venus missions face stiff competition from proposals ranging from a lunar sample return spacecraft to explorations of the moons of Saturn.
This year “started down,” Grimm said at the opening of the VEXAG meeting, “but it’s been mostly up.”