Interstellar Probe How-to
I was listening to the April 22 2009 edition of the Skeptic’s Guide to the Universe podcast a some time ago. They had on Seth Shostak, senior scientist at the SETI Institute, talking about doing an interstellar probe. In addition, Bob Novella did a blog post on the subject. The major point I got from the SGU interview and Bob’s blog post, was that Seth thinks we could do a probe to another solar system. More recently, Matt Springer at Built on Facts had some thoughts on interstellar travel as well. The reason I am only just now blogging about it is because 1. I’ve been busy at work and 2. I wanted to do more than just say I’m very skeptical of the idea. I like the idea, there is nothing physically impossible about it, so why not figure out how to make it happen and see if my feelings of skepticism are merited?
So go read (or reread) Bob’s blog post then come back. I’ll wait. Waiting…Waiting…
Back? Got it? Good.
Now remember, this whole thing is not ready for prime time, it is a crazy idea. But it might just be crazy enough to work.
We want a spacecraft that will be doing one tenth the speed of light, visiting an interesting star system with planets. Turns out there are a few such systems in our stellar neighborhood. We’ll need a really good rocket to get us up to speed.We’ll need lots of support from many people, including scientists and especially certain people in very high places.
If I understand Seth’s desired spacecraft, we’re looking at lots of little probes providing a telepresence. I’m going to make things simpler – a general telescope observatory type spacecraft, along the lines of Hubble.
A really good reason for doing a telescope is that we can start getting really good science while the spacecraft is heading away from our solar system. A slightly different view on the universe would do wonders: better parallax measurements, perhaps a view of a few Oort objects as the spacecraft leaves the solar system, and the spacecraft is traveling at a significant fraction of the speed of light so better measurements of relativity are available. Never mind the opportunity to verify and calibrate our methods of exo-planet discovery, by looking back at our own system. And if the spacecraft dies 25 years into the mission, we still get our money’s worth in telescope time. Moreover, we currently have the technology to build a really good general purpose space observatory, as witness Hubble. I’ll leave the specifics of what instruments to have on board to the scientists, but I will point out we can do a lot with currently available instruments.
Now we have an idea of what type of instruments we’d send, we need to get the data back and commands out to the spacecraft. We’ll need a really big antenna. Again, we have the technology. It will be heavy, but I’m pretty sure we can handle it without a big R&D effort.
Next, we need power onboard. Solar won’t do so well since the spacecraft will spend most of its time where the nearest star looks pretty much like every other star. Solar just isn’t practical much beyond the asteroid belt. We’ll need more power than RTG’s normally provide. We’ll need a good nuclear reactor. But before I go into anymore on the power plant, lets talk propulsion.
We need to get up to speed leaving the Solar System, then we’ll need to slow down when we get to our destination. Chemical rockets like I deal with on a daily basis won’t cut it. The nuclear based rockets being developed by the U.S. in the 60’s will not cut it either, these engines just do not use the energy very efficiently. A technology called “fission fragment rockets” holds some promise, and actually looks to be better than fusion on several levels. Fusion might work. Seth talks about the Bussard Ramjet. The Bussard ramjet concept requires fusion – it collects fusion materials from the interplanetary medium or interstellar medium, fuses them, and sends everything out the rocket nozzle. But the Bussard Ramjet is not promising for accelerating to a significant fraction of light speed relative to the local “wind”, they are however, great for slowing down.
The real problem with any nuclear rocket engine is that they do not exist and we still have some serious engineering problems that need to be worked out. Confinement and thermal issues are the primary obstacles, and even some of the proposed solutions are not sure to generate useful thrust through the nozzle. Again, I am interested in what we need to make it happen. There are no obvious science show stoppers. The gap is between the science and the engineering. We’ll need a massive program of nuclear R&D. And not just for one nuclear technology, but for multiple nuclear technologies.
A vast program of nuclear rocket development brings us to a few huge problems. First the reason why NASA and the U.S. Air Force quit nuclear rocket technology development is the Nuclear Test Ban treaty, and even if that can be worked out there is the Outer Space Treaty. We’ll need some serious diplomatic initiatives and international cooperation to do significant nuclear rocket work. The second problem is that large scale nuclear rocket development on the surface of the Earth is an ecological disaster. I don’t particularly want a large scale nuclear rocket development program in my backyard, and neither do certain powerful environmental lobbies. Third, the rocket testing needs to occur in an environment (vacuum!) that the rocket will operate in, several proposed nuclear technologies require vacuum to work. There are places off the Earth where one could do all the nuclear research desired and not measurably alter the radiation environment and get the right environment for the rocket testing. Any place outside the Earth’s magnetosphere will work. L4, L5, and possibly the lunar surface would be excellent choices.
If we are to develop a fusion rocket in space we also need a way to move large numbers of people and materials to the rocket test area. That means a robust space faring infrastructure. Not a single Shuttle 2.0, or ISS 2.0, but rather lots of different boosters, reentry vehicles, space stations, fuel depots, asteroid and lunar resource extraction. And a more diversified set of astronauts – mechanics, welders, machinists, engineeers, middle managers, plumbers, cooks, janitors and every other trade and profession that makes communities viable. The last part – a robust space faring infrastructure requires low launch costs. There are a number of people and companies trying to make that happen.
Now that I’ve laid out what is required, how do we get there? A robust space faring infrastructure is beginning. Bigelow and SpaceX have plans for and are doing demonstrations of space infrastructure. SpaceX and other smaller companies are developing lower cost launch systems. It won’t be tomorrow, but private enterprise is moving towards a robust space faring infrastructure.
Nuclear development can move forward right now, there is a lot of R&D that can happen on the ground in a safe manner and without violating any treaties. Some is already underway. More can and should be done. It won’t be the engine(s) used on the interstellar trip, but small scale demonstrations and better large scale nuclear power plants would be a big help. Once the space infrastructure is in place the R&D can scale up to large scale fusion rocket development on orbit.
As the technology groundwork is being done, diplomatic and legal efforts would need to be underway to clear any legal and diplomatic obstacles to developing peaceful nuclear technologies.
As the nuclear rockets are developed, key technologies in the Bussard Ramjet, such as the collector, can be developed and proven. A fusion rocket and other technologies would then be merged into the actual Bussard ramjet development.
Now that we have some idea of what the spacecraft requires and what technology developments we need, what does the mission look like? I’ll get to that in a future post.