5 ms·

A favorite of mine is Thrust Augmented Nozzle or TAN, where, at low altitudes, extra propellant is injected into the nozzle (not the chamber) to prevent flow se

A favorite of mine is Thrust Augmented Nozzle or TAN, where, at low altitudes, extra propellant is injected into the nozzle (not the chamber) to prevent flow separation and to increase thrust, albeit at lower specific impulse. Think of it as a bit of an afterburner for a rocket engine. https://www.aerodefensetech.com/component/content/article/adt/tech-briefs/mechanics-and-machinery/4553 https://www.aerodefensetech.com/component/content/article/ad... More thrust even at lower specific impulse at the start of the flight can save you a significant amount of gravity loss, engine mass etc.

jhgb 5y ago
A similar, but much more useful thing for the future seems to be LANTR, a.k.a. the only practical nuclear rocket engine we know of. At the very least it doesn't waste all oxygen from water mined on other bodies of our solar system like traditional pure-hydrogen NTRs do. And its average impulse density of propellant is way higher, of course.
- kurthr 5y ago
  I had to look that up. This was the nicest explanation I found, but if you recommend a different one, please post. I also found stuff on Kerbal, but I'm not clear how real that is. http://www.astronautix.com/l/lantrmoonbase.html http://www.astronautix.com/l/lantrmoonbase.html
  - jhgb 5y ago
    There's a NASA TR about it: https://ntrs.nasa.gov/citations/19950005290 https://ntrs.nasa.gov/citations/19950005290
- credit_guy 5y ago
  This is solving a different issue. Aerospike engines deal with the fact that rocket engines need to be different in an atmosphere vs in vacuum. Nuclear thermal rockets (NTRs) are not really envisioned for being used in the atmosphere, the risk of a blowup is too high. I consider them a wonderful technology which could really open up new possibilities, but we first need to nail down the challenge of affordably getting to orbit.
  - jhgb 5y ago
    Except LANTR solves a very similar problem, which is the requirement for different performance parameters at the beginning and at the end of a rocket flight (high thrust and propellant density in first stage, low thrust and high Isp in the second stage) in a single stage vehicle. And I mentioned it because its way of operation is very similar to the thing describe above, i.e., injecting something extra into the nozzle, so it reminded me of it. Not because I consider it comparable to using aerospikes on Earth (I'm not convinced that's useful at all) but because this is one of the few such variable Isp options that appears to provide any useful benefits at least somewhere (even if it's not on Earth).
  - pfdietz 5y ago
    The problem with NTRs in the atmosphere isn't the risk of blowup, it's that their thrust/weight ratios are just terrible. And in the atmosphere, it's early in the launch, so Isp is not important.
    - panick21_ 5y ago
      I don't think it necessary true that NTRs have terrible trust/weight. Depending on what your 'fuel'. You potentially lose ISP of course, but your Thrust would go up. It also depends on the engine configuration, you could do much better in terms of weight and density.
      - pfdietz 5y ago
        Thrust of a rocket is a function of nozzle throat and exit areas and thrust chamber pressure, and is (ideally) independent of the density of the propellant. Engines used on a first stage typically have high thrust, but that's because they're designed with large throats, not because of the propellant they use. A dense propellant does allow the pumps to be smaller. But I don't think that's going to help much in a NTR, since the reactor itself is heavy. The problem with an NTR is the difficulty of getting high mass flow past very thin fuel elements (the thinness necessary for high heat transfer) without destruction of the fuel elements by that flow. The thin fuel elements also ensure some fission products will escape and be carried off in the propellant.
trhway 5y ago
>A favorite of mine is Thrust Augmented Nozzle or TAN, where, at low altitudes, extra propellant is injected into the nozzle (not the chamber) and that gets close to my favorite - air-augmenting regular rocket engine. Very simple and bumps up your thrust and ISP up to 2-3x http://www.astronautix.com/g/gnom.html http://www.astronautix.com/g/gnom.html

jhgb 5y ago

A similar, but much more useful thing for the future seems to be LANTR, a.k.a. the only practical nuclear rocket engine we know of. At the very least it doesn't waste all oxygen from water mined on other bodies of our solar system like traditional pure-hydrogen NTRs do. And its average impulse density of propellant is way higher, of course.

kurthr 5y ago
I had to look that up. This was the nicest explanation I found, but if you recommend a different one, please post. I also found stuff on Kerbal, but I'm not clear how real that is. http://www.astronautix.com/l/lantrmoonbase.html http://www.astronautix.com/l/lantrmoonbase.html
- jhgb 5y ago
  There's a NASA TR about it: https://ntrs.nasa.gov/citations/19950005290 https://ntrs.nasa.gov/citations/19950005290
credit_guy 5y ago
This is solving a different issue. Aerospike engines deal with the fact that rocket engines need to be different in an atmosphere vs in vacuum. Nuclear thermal rockets (NTRs) are not really envisioned for being used in the atmosphere, the risk of a blowup is too high. I consider them a wonderful technology which could really open up new possibilities, but we first need to nail down the challenge of affordably getting to orbit.
- jhgb 5y ago
  Except LANTR solves a very similar problem, which is the requirement for different performance parameters at the beginning and at the end of a rocket flight (high thrust and propellant density in first stage, low thrust and high Isp in the second stage) in a single stage vehicle. And I mentioned it because its way of operation is very similar to the thing describe above, i.e., injecting something extra into the nozzle, so it reminded me of it. Not because I consider it comparable to using aerospikes on Earth (I'm not convinced that's useful at all) but because this is one of the few such variable Isp options that appears to provide any useful benefits at least somewhere (even if it's not on Earth).
- pfdietz 5y ago
  The problem with NTRs in the atmosphere isn't the risk of blowup, it's that their thrust/weight ratios are just terrible. And in the atmosphere, it's early in the launch, so Isp is not important.
  - panick21_ 5y ago
    I don't think it necessary true that NTRs have terrible trust/weight. Depending on what your 'fuel'. You potentially lose ISP of course, but your Thrust would go up. It also depends on the engine configuration, you could do much better in terms of weight and density.
    - pfdietz 5y ago
      Thrust of a rocket is a function of nozzle throat and exit areas and thrust chamber pressure, and is (ideally) independent of the density of the propellant. Engines used on a first stage typically have high thrust, but that's because they're designed with large throats, not because of the propellant they use. A dense propellant does allow the pumps to be smaller. But I don't think that's going to help much in a NTR, since the reactor itself is heavy. The problem with an NTR is the difficulty of getting high mass flow past very thin fuel elements (the thinness necessary for high heat transfer) without destruction of the fuel elements by that flow. The thin fuel elements also ensure some fission products will escape and be carried off in the propellant.

trhway 5y ago

>A favorite of mine is Thrust Augmented Nozzle or TAN, where, at low altitudes, extra propellant is injected into the nozzle (not the chamber) and that gets close to my favorite - air-augmenting regular rocket engine. Very simple and bumps up your thrust and ISP up to 2-3x http://www.astronautix.com/g/gnom.html http://www.astronautix.com/g/gnom.html