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I'm skeptical too, but DARPA is saying the DRACO program is for getting to/from Mars quickly: > The DRACO program intends to develop novel nuclear thermal prop

I'm skeptical too, but DARPA is saying the DRACO program is for getting to/from Mars quickly: > The DRACO program intends to develop novel nuclear thermal propulsion (NTP) technology to enable time-critical missions over vast distances in cislunar space. Unlike propulsion technologies in use today, NTP can achieve high thrust-to-weights similar to chemical propulsion but with two to five times the efficiency. This enables NTP systems to be both faster and smaller than electric and chemical systems, respectively. The propulsive capabilities afforded by NTP will enable the United States to maintain its interests in space, and to expand possibilities for the National Aeronautics and Space Administration (NASA)’s long-duration human spaceflight missions (i.e., to Mars). Because of the ability to transit space faster than other propulsion systems, the NTR engine can return astronauts to Earth much faster in case of an emergency and similarly ensure reduction of overall trip time and exposure to deleterious impacts to astronaut health which come with long-term spaceflight.

jhgb 4y ago
> but with two to five times the efficiency I suspect from the number that they're talking purely about Isp. Once one performs a whole system analysis, it's much less rosy for (non-LA)NTR.
- robonerd 4y ago
  I agree. Furthermore, besides the mention of Mars they're also talking about cislunar space in that same paragraph, but chemical propulsion seems sufficient in cislunar space. It's only takes a days to return from the moon with chemical propulsion, which proved sufficient in the past.
  - jhgb 4y ago
    LANTR would improve performance of lunar landers/cislunar shuttles, especially for variable specific impulse which is what LANTR could plausibly do without much trouble -- start with high oxygen flow for high thrust and high propellant mixture density, decrease oxygen flow later in flight for higher terminal Isp. This brings you the performance of a multi-stage vehicle without staging, and LANTR can even with high oxygen flow deliver Isp significantly higher than what hydrolox has, with propellant density several times higher than what pure-hydrogen NTR gives you. I've thought about trying to optimize the performance of such a variable Isp vehicle, but it requires calculus of variations skills that I'm lacking at the moment. I guess I need to take a look at that. But there's a decent chance that with a such a vehicle, you could move from the "we need to mine ice on the Moon" to the "we just need to extract oxygen from lunar soil; we can bring hydrogen from LEO" territory, which would be a win for lunar flights (for example you wouldn't be limited to polar region bases where you'd need to mine water to get back home).
  - deleted 4y ago
    [deleted]
mlindner 4y ago
It's not for getting to/from Mars quickly. It's for giving money to congressional districts quickly.

jhgb 4y ago

> but with two to five times the efficiency I suspect from the number that they're talking purely about Isp. Once one performs a whole system analysis, it's much less rosy for (non-LA)NTR.

robonerd 4y ago
I agree. Furthermore, besides the mention of Mars they're also talking about cislunar space in that same paragraph, but chemical propulsion seems sufficient in cislunar space. It's only takes a days to return from the moon with chemical propulsion, which proved sufficient in the past.
- jhgb 4y ago
  LANTR would improve performance of lunar landers/cislunar shuttles, especially for variable specific impulse which is what LANTR could plausibly do without much trouble -- start with high oxygen flow for high thrust and high propellant mixture density, decrease oxygen flow later in flight for higher terminal Isp. This brings you the performance of a multi-stage vehicle without staging, and LANTR can even with high oxygen flow deliver Isp significantly higher than what hydrolox has, with propellant density several times higher than what pure-hydrogen NTR gives you. I've thought about trying to optimize the performance of such a variable Isp vehicle, but it requires calculus of variations skills that I'm lacking at the moment. I guess I need to take a look at that. But there's a decent chance that with a such a vehicle, you could move from the "we need to mine ice on the Moon" to the "we just need to extract oxygen from lunar soil; we can bring hydrogen from LEO" territory, which would be a win for lunar flights (for example you wouldn't be limited to polar region bases where you'd need to mine water to get back home).
- deleted 4y ago
  [deleted]

mlindner 4y ago

It's not for getting to/from Mars quickly. It's for giving money to congressional districts quickly.