Mailbag - 5 April 2015

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If the funding for the International Space Station gets repurposed, could the ISS itself also get repurposed? I’m sure the answer must be no but I still have to ask. If the ISS was fit with ion thrusters, could it be used like Hermes?
— Jesse

Sadly, you're intuition is correct, or at least NASA is posturing in that regard. In response to news that Russia plans to pull out of the ISS, INASA Administrator Charles Bolden said astronauts aboard the American section of the station would make an "orderly evacuation" if that were to occur. The trouble is that many of the safety and backup systems used to keep astronauts aboard the orbiting laboratory safe are spread throughout the entire station. Removing half of it could put our men and women at risk.

The notion of using the ISS in a manner similar to the Hermes from Andy Weir's The Martian is an intriguing idea, but technology simply isn't ready yet. For those who haven't read Weir's (gripping!) story, the Hermes is a reusable spacecraft designed to shuttle astronauts back and forth to Mars numerous times over the course of years. In order to accomplish this with the minimum amount of fuel, it employs a technology known as the ion engine. Instead of basically starting an explosion in the back of the spacecraft as chemical rockets do, ion thrusters basically just throw charged particles out the back and rely on conservation of momentum to push the ship forward. They've been used on a number of missions, including Dawn and Hayabusa.

The problem is, the ISS is enormous. It has a mass about 350 times larger than Dawn, and that would certainly need to be even heavier for a trip to interplanetary space. Ion thrusters simply can't provide even close to enough power yet...


You mentioned the risk to the project to capture an asteroid in last week’s Weekly Space Hangout, due in large part to the long time prior to its execution. There are at least two presidential administration turnovers before that time, increasing the opportunity for changes or cancellation.

I agree with that, but I think there may be a mitigating perspective here. Maybe think of capturing an asteroid as a mining mission, mining technology development. I think that may actually increase the probability of a successful mission. It’s about the economy, a harder project to cut.
— James

Mining an asteroid is certainly a popular idea these days. Private companies like Planetary Resources hope to turn this into a viable business model, but haven't demonstrated that capability yet. I don't think that it's the pivot that the Asteroid Retrieval Mission (ARM) needs, though.

ARM is trying to spur human spaceflight beyond Low Earth Orbit once again, but asteroid mining is definitely going to be a task better carried out by robots. It's going to be slow, arduous, and extremely dangerous work - exactly what we use robots for even here on Earth. And robots will most likely be cheaper, increasing any potential return on investment.

I'm also not sure that turning it into a mining effort would save it from either Congress or a future president. Material and monetary returns in the foreseeable future, while possibly significant for a company like Planetary Resources, will be vanishingly small in the overall production of the United States. Worse yet, mining asteroids might seem like an even more pie-in-the-sky idea than just exploring them and thus draw the ire of some lawmakers even more rapidly.

Finally, there's the ongoing legal question of who owns the stuff in space. The Outer Space Treaty of 1967 states explicitly: "outer space is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means." How that applies to space mining is untested legal territory.


The part about Ceres’ white spots on a recent episode of the Weekly Space Hangout was especially riveting. I was resigned to just exposed ice. But if there is some out gassing or plume effect, what the heck would cause it? There is no gravitational tidal effect. A mystery, lets see what the mission brings us. I hope they are taking pictures on the dark side approach to see if something shows up on the edge using the back-lighting technique.
— Valentin

The white spots on Ceres are indeed fascinating! To be clear, other than the existence of two white spots in images captured by the Dawn navigational camera, nothing is known about this area for sure. But recent indications that the features might extend vertically above the rim of the crater and change in brightness over the course of the day is certainly exciting.

This actually isn't even the first indication of possible plumes at Ceres. Last year, scientists using NASA's Herschel Space Telescope reported a clear detection of water vapor above the surface of the dwarf planet. Their explanation is the most probable one: that heat from the Sun causes ice deposited on the surface to sublimate during times of the (Ceres) year when the dwarf planet is closer to it. This could also account for the daily variation, as temperatures on the surface would vary based on the local time of day, just like they do here on Earth!

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