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Update on Project Prometheus
Aglassis writes "It appears that NASA is not backing down from their nuclear space initiative. Project Prometheus has recently started a new web page (under JPL) and NASA is finishing up a period of public comment (last session today). Currently Northrop Grumman is contracted to begin preliminary design of the spacecraft until 2008 for NASA (the reactor will be built by the Department of Energy's Division of Naval Reactors--the folks who control all US submarine and aircraft carrier nuclear reactors). Early specs are that it will be 60 meters long, have a 30,000 kg mass, use a 100 KW reactor using Brayton cycle gas turbines, be powered by ion thrusters with a 7000 second specific impulse, and have a science payload of 1500 kg. Early mission plans for Prometheus 1 (Jupiter Icy Moons Orbiter) indicate that the spacecraft would orbit Callisto, Ganymede, and Europa individually, and perhaps have a lifespan of about 20 years."
"Prometheus Nuclear Systems and Technology will focus on enabling NASA missions by researching and developing nuclear sources that will provide power to innovative scientific instruments and robotic systems, large and small propulsion systems that run on electricity and high-speed communications systems. The nuclear power sources would allow us to extensively explore our closest celestial neighbor, the Moon, as well as Mars and other destinations. Eventually, these power sources would support human explorers as they travel through space and explore other worlds.
= mi ssions
The first proposed mission within Prometheus Nuclear Systems and Technology would be a mission to Jupiter, the Jupiter Icy Moons Orbiter (JIMO), which represents a new class of mission capabilities far beyond those possible with current power and propulsion systems. Powered by a space nuclear reactor and propelled by electric ion engines, the spacecraft would make up-close, long-term orbiting visits to three of the solar system's most intriguing moons- Europa, Ganymede, and Callisto. Beneath their icy surfaces, these moons may contain oceans of water that could have provided an environment that may have harbored life."
http://prometheus.jpl.nasa.gov/index.cfm?pageL1
Beats the heck out of me what that has to do with militarizing space. Besides, IMO, nuclear power is a lot less environmentally dangerous than other power sources except maybe solar energy (which might not work when you're x billion miles from the sun).
--- Grow a pair, liberals... stop letting the Republicans bully you!
There are open and closed versions of the Brayton cycle engine.
=Smidge=
what do you think absorbs the readiation from the sun? (hint, its our atmosphere) that big ball in the sky that is the solar systems largest reactor (although its fusion, not fission). Honestly, do you think it's light that heats the earth? no, it radiation. Any radiation from a little spacecraft up in space is miniscule!
What are we going to do tonight Brain?
You are 100% correct. The large panels are radiators to dissipate excess heat. Large radiators are a standard feature in designs for space-going reactors, since the conversion from thermal energy to electrical energy is far less than 100% efficient.
Our local observatory (with live night-sky camera) is Gummint-funded. This leads to some interesting effects.
Much of their computing equipment has been scrounged - and doesn't appear on any equipment manifests - because there was no budget for it. They have a Pentium-90 driving (pointing) their main 'scope with a backup P-90 literally sitting on the next shelf in case it dies.
The few pieces of gear that they do get grants for are typically extremely fancy. On the rare occasions when ThePowersThatBe say "yes, you can have a computer to process the incoming images," then the cost of that actual computer system and absolutely nothing else is almost immaterial as long as it fits certain criteria.
So... in the room to the left of the one housing the P-90 sits a you-beauty glow-in-the-dark (well, not literally, it would cause backscatter) state-of-the-art box with double overhead ThermalTakes and all the trimmings. Just one. And I bet they crammed memory and disks into that baby's purchasing spec until the chassis groaned under the weight.
When Mark Shuttleworth gave his amazing talk at LCA2005, one of the things he mentioned was that the Yanks didn't want their astronauts (also going up in the Soyuz with Mark) flying to Baikonur in a rattly old Tupelov transport lest it unexpectedly drop out of the sky en route, but rather than come out and say so directly they came over all clever and simply pointed out that NASA regs forbade their astronauts to travel without seatbelts, which they knew the Tupelov wasn't fitted with. This was a mistake. On the day, the astronauts were marched out to the Tupelov, and aboard - and into a minibus in the cargo bay, where they sat and wore the minibus's seatbelts for the duration of the trip.
BTW, when the video DVD from LCA2005 gets published, bend heaven and earth to get yourself a copy. It's well worth-while for Mark's presentation alone ("Welcome to Khazakstan!"), and there are many other excellent presentations on it (Keith Packard explaining the sport of Window Hurling, for example, or E'dale demonstrating how to collapse a penguin's skull).
The point in that story which I wanted to use as an illustration here was that the minibus wasn't put aboard the transport for the astronauts' benefit. There was a budget for flying the Tupelov - pilots, fuel, landing fees and so on - but no budget for getting from the airport to where they were staying. So the van (which fell under the base's budget, so was financially covered) was fuelled up and driven aboard the Tupelov for use as a taxi while the transport 'plane was prepped for the return flight. In terms of working around bizarre regulations, NASA or not, the Americans really were amateurs playing in a professional field. (-:
Got time? Spend some of it coding or testing
The move to fission is driven by a desire to get more power (even a large RTG will only produce a few hundred Watts, versus the kilowatts they expect to get from a reactor). I don't know exactly what the trade-offs are with using Brayton cycle vs thermoelectric (or thermionic) conversion. The Russians have flown a number of thermionic nuclear reactors (the Topaz series), and they seemed to work fairly well. I suppose it's possible that Brayton cycle reactors are more efficient than thermoelectric/thermionic conversion. But even if you assume a (highly unlikely) 90% conversion efficiency, a 100kW reactor would leave you with 10kW of thermal energy to dump. At this point it's probably worth noting that even the most high-power satellites we currently fly (the Boeing 702 comm-sat) operate on a mere 15kW of power. So you're talking about being able to radiate as much energy as most satellites generate in total. And as I said, that's based on some pretty optimistic assumptions about the efficiency of the Brayton cycle.
In case you didn't realize, Uranium is the 8th most common material on the planet... Taking a few tons off of it won't do any good. There's enough uranium to last the damn planet for the next 2000 years at least. Don't argue with me, I researched the damn thing two months ago. :)
Due to financial difficulties, the light at the end of the tunnel has been turned off.
A good point. In fact, thermal design for spacecraft (at least at the preliminary stages) is typically carried out under the assumption that all of the electrical energy not leaving the spacecraft as RF radiation is converted into thermal energy.
The two energy expenditures I can think of that don't yield waste heat are the propulsion system (ideally), and the radios (again, ideally).
Unfortunately, both of those items are less than ideal. It's not uncommon for a spacecraft transponder to be on the order of 20% efficient (or worse). Likewise, the ion propulsion systems they are planning on using for Prometheus have an electrical->thermal conversion efficiency of around 70-80%. Which for a 20kW thruster (e.g. the proposed NEXIS thruster) means 4kW+ of waste heat.
Of course, I expect it would be possible to use a significant portion of that to heat the propulsion fuel.
The current proposals for Prometheus involve nuclear-electric propulsion rather than nuclear-thermal propulsion. I don't believe that heating the propellant in a NEP system helps (although I'm not really a propulsion expert, so I'm quite prepared to be corrected on this).