Where are we going in space?
by Philip Stooke
|It is unreasonable to think that the first flight of the new system can go directly to an asteroid, and also that all that cost and effort would result in only one asteroid mission.|
First we have to start with hardware. The Constellation program arising from President Bush’s Vision for Space Exploration in 2004 had five major components: a small rocket (Ares 1) for crew launches and a heavy-lift launcher (Ares 5) for full exploration missions, a crew vehicle (Orion), a lunar lander (Altair), and whatever was needed for lunar surface operations, including advanced rovers for short science missions or habitat, rover, and power systems for an outpost. That’s a lot of hardware and the full assemblage was deemed unaffordable. The Augustine study of 2009 suggested omitting the lunar components, reducing the cost enough to be feasible while still allowing asteroid or Mars orbit missions. Obama has modified this idea further—his new program doesn’t have a name yet—by scrapping the Ares rockets and replacing them with commercial launchers for Earth orbit access and a brand new heavy-lift vehicle for exploration. A future human exploration vehicle, either modified from Orion or taking its place, is also needed but has not yet been defined.
The next few years of NASA human spaceflight operations are clear. The shuttle will be retired very soon and astronauts will ride to and from the International Space Station on Russian Soyuz spacecraft. That would have happened under Constellation, and it will be just the same under the new plan. Some time around 2015 there may be a transition to a commercial provider, either SpaceX’s Falcon 9 and its Dragon capsule if they fly successfully, or a competitor flying on another human-rated launcher. The new heavy-lift vehicle design is supposed to be selected in 2015, though I would not be surprised if this important decision was moved to an earlier date. By the early 2020s the large new launcher should be ready, and at about the same time the new crew exploration vehicle should also be approaching its initial flight. That date might have to move a year or two down the line, but there isn’t much point having the large launch vehicle ready long before its payload.
So far this is not very different from what Constellation was supposed to have accomplished by that date, except that the lunar hardware has been omitted. Constellation would have flown its first lunar mission in 2019 according to the original plans, though it had become clear to most observers that it would be delayed by several years at least. So what can the new system accomplish in the early 2020s? In what follows I assume that the heavy-lift launcher and a crew exploration vehicle are available by that time, and that work on radiation shielding and life support has matured enough to permit some exploration beyond Earth orbit at about the same time.
President Obama has suggested that a human asteroid mission should take place in about 2025, and a trip to Mars orbit a decade later. It is unreasonable to think that the first flight of the new system can go directly to an asteroid, and also that all that cost and effort would result in only one asteroid mission. Just as President Kennedy’s directive to land on the Moon resulted in nine lunar flights rather than one, we would not build all that hardware and develop all those procedures just for one mission, and then wait a decade for the Mars trip. It is more realistic to expect some early test flights of the asteroid mission hardware, like the Apollo 8 and Apollo 10 lunar orbit missions preceding the first lunar landing, and then we could reasonably anticipate at least a decade of asteroid exploration leading up to the first Mars voyage.
|Every encounter with an asteroid would be different, the science would be important, and the spectacle would be stunning.|
This now becomes very speculative, but the following might make sense as a plausible sequence of missions. The first test flights in about 2021 would presumably be Earth orbital missions like Apollo 7 and Apollo 9, but longer voyages would be needed for better simulation of a true asteroid mission. To visit an asteroid, the spacecraft would use its upper stage rocket three times: one burn to leave Earth, a second to match the orbit of the asteroid, and a third to return home. A lunar orbit mission follows the same pattern of rocket burns and is the most obvious choice for a test flight. Thus I would anticipate that in roughly 2022 a first lunar orbital mission might be undertaken. It might only spend a few days in lunar orbit, but it would test navigation, communications, and other spacecraft functions needed for an asteroid mission, and perhaps undertake some research or exploration work as well. For instance, it might enter an elliptical orbit with its highest point over a pole, allowing it to serve as a communication relay with a robotic lander or rover in a shadowed polar crater, a location invisible from Earth.
Asteroid missions would typically last for several months, so longer test flights would be very desirable. I might anticipate a second lunar orbit mission in 2023 lasting a month or more. It could also perform some lunar research from orbit. The longer stay might be suited to a communication relay role for, or direct human control of, two or three sample return lander or rover missions on the far side. Photography or other forms of remote sensing are always possible, and would also be important during an asteroid visit, so the lunar orbit mission might be used to calibrate those instruments. Very low passes over the surface might allow the orbiter to collect dust if, as we suspect, it can become electrically charged and levitated. A spacecraft called LADEE will examine this dust in 2013, but this human test mission could sample the dust and bring it back to Earth.
Now the stage would be set for the first human journey into deep space. An initial flight might not visit an asteroid at all, but simply make a very long looping path out to about ten times the distance to the Moon and back, a journey lasting several months. This would test communications and navigation over longer distances and verify the re-entry from deep space, and it would easily break the human distance record from Earth. This flight might happen in about 2024, and when it was accomplished safely everything would be ready for the first flight to an asteroid in 2025.
Small asteroids pass relatively close to Earth fairly often, so target selection would involve identifying a suitable candidate with an appropriate orbit and flyby distance. At this stage I could not guarantee that a suitable asteroid would be available in 2025 or any other specific year, but it is very probable that one or more would be available in most years. The further one is willing to travel, the greater likelihood there is of finding a good target in a given year. Assuming a good candidate was available in 2025, a mission would leave Earth on a path that brought it close to the asteroid. A rocket burn would change the spacecraft’s velocity to match the path of the asteroid, and the two objects would move on parallel paths for the duration of the visit. The most likely targets for a mission like this are small—only a few hundred yards across—with gravity so weak that the spacecraft would not appear to be orbiting the asteroid. Eventually another rocket burn would send the crew back to Earth.
On the first human mission to an asteroid the crew might not attempt to visit the surface. Detailed observations of the little rocky world from all sides would of course be made, photographically and by other means. Various instruments might determine surface composition, and radar might probe the interior to determine its inner structure. The crew would almost certainly deploy small instrument packages or sample return devices on the asteroid. On the other hand, the ease of movement in this low gravity environment might permit at least one surface sortie by the crew, including sample collection, on the first mission. If not, that would happen on the second mission, a year or two later. Adequate radiation shielding would be essential for any of these remote exploration missions, so it would be thoroughly tested on this trip.
|The moons of Mars can be visited without an expensive lander, and they are themselves very interesting targets.|
Decades of telescopic and radar observations and several robotic asteroid missions to date have shown that asteroids are very varied in size, form, and composition. Some are rocky, some carbon-rich, and others metallic, and some may be monolithic slabs of rock while others are probably loose piles of rubble. Some have their own little moons. Some might be burned-out comets, exotic worlds once rich in ice but dried out by frequent passes near the Sun. Candidate asteroids for human missions would be selected so that a variety of targets could be visited. If these missions were flown at roughly two-year intervals for a decade or more, a good sample of the diversity of near-Earth objects could be explored. Every encounter would be different, the science would be important, and the spectacle would be stunning.
As more asteroids are visited, we may imagine that our growing experience of deep space flight would allow voyages to more distant targets until round trips on the order of a year long were being undertaken. These missions would serve as test flights for the next destination, Mars. Or rather, not Mars itself but the satellites of Mars, Phobos and Deimos. These small moons, about 20 and 12 kilometers across respectively, would be similar in some respects to the asteroids that had been visited in previous years except that they are substantially larger, with more noticeable but still very weak gravity.
Why go to Phobos and not to Mars itself? Mars will be a difficult place to land on and, like the Moon, it will require an expensive lander, so that goal is deferred until the technology is ready and the budget can accommodate it. However, the moons of Mars can be visited without an expensive lander, and they are themselves very interesting targets. Phobos is covered with long narrow valleys and chains of craters, and Deimos is very smooth. Why are they so different? Are they made of the same material? Are they fragments blasted off Mars in titanic impacts long ago or objects from the asteroid belt captured while passing the planet? And can we find fragments of Mars on their surfaces? We have meteorites from Mars here on Earth that had to pass the moons on their way to us. Many more bits of Mars, kicked up by impacts over billions of years, may litter the surfaces of these little moons.
Phobos and Deimos may have another role to play in Mars exploration. Astronauts in a habitat on one of the moons might control rovers on the planet in real time, collecting samples for analysis on the planet or launching them to be collected by the crew in orbit. Those operations could be sustained over more than just one visit, and would differ from finding Mars rocks on Phobos in that we would know where they came from on the planet. I suggested at a conference at NASA Ames Research Center a couple of years ago that a series of robotic sample collection missions to Mars might cache their samples on Phobos over the course of a decade or so. Eventually they would be picked up by astronauts and returned to Earth. At the time there was no specific plan to send people to orbit Mars, but now there is.
Finally, when both funding and technology are available, a crew-carrying lander can be built and flown to Mars. The long sequence of lunar orbit, asteroid, and Phobos/Deimos missions will have expanded our capabilities and tested every component of the mission up to that point, as well as doing a lot of valuable scientific research along the way.
Of course, the speculative sequence of missions laid out here is missing something. Moon landings are conspicuously absent because money was saved by not building a lunar landing vehicle or other surface equipment. The absence of lunar landings in the new program is vociferously opposed by some people, but strongly supported by others. In my opinion the president has been badly advised on this point. It’s true that we have already been there, but much remains to be done on the Moon. We know far more about the Moon now than we did even a decade ago, particularly regarding the presence of water and other resources in polar craters. Geologists want to explore many fascinating areas not visited by Apollo, and there is considerable interest in learning to acquire and use lunar resources. Learning to live and work on the Moon using local resources may be the first step in expanding humanity to other worlds. The Moon is important, and I would suggest it is quite likely that a future administration will restore this goal when money becomes available.
|The absence of lunar landings in the new program is vociferously opposed by some people, but strongly supported by others. In my opinion the president has been badly advised on this point.|
But what if that does not happen? There’s more than one way to get to the Moon, and another possibility arises when we remember that space is increasingly an international endeavor. While Constellation was under development, international partners were planning contributions to it just as they had made contributions to the International Space Station. For instance, the Canadian Space Agency was contemplating supplying rovers or other surface hardware, and the European Space Agency was planning an automated cargo lander to help supply an outpost. One possibility that may be imagined (since this entire article is a flight of fancy) is that lunar missions could become the international component of a future global exploration program. This would be promoted and negotiated as the ISS partnership was. Perhaps the ESA cargo lander design could be modified to carry astronauts, but any other space-faring nation or private sector entity could make a contribution in this area as well.
Now we can imagine a human lunar expedition operated jointly by NASA and these other partners. The lander could be flown into lunar orbit without a crew. NASA’s crew exploration vehicle would follow it, go into orbit and dock with it. Two astronauts would descend to the surface in the lander for Apollo-style activities at an interesting site, and then return to orbit. A single month-long flight might allow two landings at different locations in separate landers with separate two-person crews. A system like this could conceivably include a spare lander to provide rescue capability, something Apollo never had. This system might also be augmented by delivering supplies including a rover to the target site on a cargo lander before the crew is launched, a capability discussed for Apollo but never implemented. Ultimately the system could support a small outpost if that was the desired goal.
This view of a possible new space program gives NASA the noble goal of moving outwards to the asteroids and Mars, but rather than closing down the lunar program it makes the return to the Moon an international endeavor. NASA’s contribution to any lunar flight would be the same as its first test flights in the early 2020s, so no new hardware would be needed. The flight rate could be kept low to hold annual costs to a reasonable level.
If all these daydreams came to pass, the 2030s would be a very exciting and productive time in space. The decade would begin with asteroid missions flown at intervals of about two years. The hypothetical lunar landings just mentioned might be flown in the intervening years. This flight rate, one launch per year alternating between asteroids and the Moon, would be less expensive than the two or three lunar flights a year required by Constellation to maintain a lunar outpost. In mid-decade the first Mars orbital mission would occur, and this might be repeated at intervals of several years, interspersed with additional asteroid and lunar exploration flights.
|If all these daydreams came to pass, the 2030s would be a very exciting and productive time in space.|
Would the public quickly tire of the spectacle, as supposedly happened with Apollo? It is debatable whether that really happened in the first place, but the world is very different now and the experience of the new exploration program would be different as well. I watched Apollo as it happened, and I don’t agree that “the public” tired of it. There isn’t one public; there are many. Most people who were interested in space exploration stayed interested, but many others were disinterested from the start. Some of those people were temporarily caught up in the novelty of Apollo, but their attention soon moved on to something else, as it always will. The problem for those who stayed interested was that media coverage became briefer and harder to find, and that served to discourage some from looking. This is very different from saying people lost interest.
Future mission coverage would be completely different. Everybody will be able to find all the information or spectacle they want from websites offering multimedia, streaming video, discussion forums, blogs and tweets, or whatever innovations replace them. The new program will be promoted more like the Mars rovers or the Cassini mission to Saturn are today, on official websites and a multitude of networking and enthusiast sites of all types. People will be watching EVAs on their phones over lunch. We may see a forerunner of this in the Google Lunar X PRIZE missions to the Moon as early as 2012. The teams most likely to make an attempt on that prize will make full use of the most current media, as publicity and public engagement are keys to revenue generation.
Much of what I have said is just speculation, and most of it lies outside the specific goals laid out recently by President Obama. But Apollo also exceeded the minimum that was called for by President Kennedy. My intention has been to show that the new mandate, translated into a reasonable sequence of missions, can offer an exciting exploration program with the potential to engage and inspire the world. This is truly, in Augustine’s words, a space program worthy of a great nation, not an end but a beginning.