# Tag Info

10

Conceptually, staging is getting rid of hardware we no longer need. Keeping useless hardware attached to the rocket is expensive, since added mass reduces acceleration. Ideally, we would want to get rid of hardware as soon as it gets useless, instead of piling it up to a "batch", which is essentially what the question boils down to. Rockets are very simple*...

8

The Everyday Astronaut just released an hour long video investigating this question. Some of the main points are: Aerospikes are especially advantageous to single stage to orbit vehicles, and current space companies are not building those. There isn't really an advantage in SSTOs compared to multi stage rockets. The efficiency advantage of aerospikes isn'...

7

How about NERVA? NERVA (Nuclear Engine for Rocket Vehicle Application) was a nuclear-thermal engine. A reactor heated hydrogen propellant and exhausted it out the nozzle. The engine was extensively and successfully ground tested. Thrust ~ 250 kN ISP ~ 840 (You didn't mention political considerations or thrust-to-weight ratio)

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tl;dr: The problem is that this idea relies on a fundamental misunderstanding of Special Relativity. $$+$$ Newton's second law of $F = ma$ doesn't work, exactly, in Special Relativity. $$+$$ But if you instead write down Newton's second law as $F = dp/dt$, where $p$ is momentum, this does work exactly (and equally for all observers), even in ...

5

The method described proposes a propulsive force based on following the gradient of the vacuum energy density. However, I see two problems There is no evidence given in the question showing that a gradient in vacuum energy exists. Even if one did exist (some location has a lower vacuum energy than another location) there is no evidence given in the ...

4

is a good ‘old fashioned ion drive, good enough? It is good enough that we use it. They have a reasonable fuel economy, as your spacecraft doesn't have to be made of mostly fuel, and a high enough thrust that your orbit can be significantly altered within a couple of months. The first three of your drives are operating on known physics, which makes it ...

4

In general, thermal rockets can in theory have very good $I_{SP}$ (around 1000s), and provide high thrust. Unlike chemical rockets, which by definition produce heavy exhaust gasses like $CO_2$, $CO$ or $H_2O$, a thermal rocket can pick any propellant. That would mean it's possible to eject pure hydrogen gas (which in the hotter cases will start to ...

4

No. LANTR didn't increase ISP either. Its advantage was that it had increased thrust (relative to both weight and cost). @rokomijic's answer gives the reason why it doesn't: Exhaust velocity ($v$) is proportional to the square root of temperature over particle mass. As: $\frac {1}{2}{\overline {mv^{2}}}=\frac {3}{2}k_{B}T.$ Chemically combining to ...

4

I'm assuming that the goal is to get to orbit with a hybrid between a nuclear turbojet and a nuclear thermal rocket. Be aware that H2O is a significantly heavier molecule than H2, so mixing your hydrogen with oxygen is unlikely to improve V_exh, even if it increases the temperature somewhat. On that basis I'm going to guess the answer is no, and that the ...

3

I'm just going to add some considerations about tidal forces, thanks to @Steve Linton for mentioning this: Crushed by the moon The tidal force (https://en.wikipedia.org/wiki/Tidal_force) from the moon is rather small, about $10^{-12} m/s^2/m$. This is not a serious problem. Crushed by the spacecraft When a spacecraft lands on the runway, it exerts ...

3

https://lifeboat.com/em/arrestor.pdf "An Orbiting Magnetic Arrest System for Rocket-Free Transportation to Earth Orbit" If transport to earth orbit could be decoupled into the two separate tasks of reaching orbital altitude and maintaining an orbit, rocket-free transportation to orbit would be possible with straightforward improvements to existing ...

2

This is one of a whole bunch of space launch ideas that all involve "loading up" a massive orbiting object of some kind with energy and angular momentum. Then you somehow attach it to a relatively small payload of some kind and transfer angular momentum and energy to the payload. As a rather extreme example, you could put a very small payload into orbit by ...

2

Notes On Prior Art I have had this concept up at wikiversity for a while now, and recently initiated a conversation with the OP on twitter, which is how this question got started. What inspired me to start thinking about it at first was a reddit comment from Dani Eder about the possibility of landing on the Moon using a metal coated track and magnetic ...

1

In response to two of your questions: Is it naturally stable? No. Tidal forces will tend to torque anything in orbit so that its long axis points in the radial direction; in order to keep your launch ribbon horizontal, you'll need active measures to counteract this. Things get worse when you realize that in the 25 seconds you need for your spaceship to ...

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