26
votes
Do larger rockets tend to have a better mass ratio due to the square cube law?
The walls of pressurized tanks in particular need to get thicker as the pressurized volume increases, so the tankage mass still increases pretty close to linearly with the tankage volume, and tankage ...
- 172k
21
votes
Accepted
Benefit of Raptor Engines
A few different factors contribute to the Raptor's higher thrust:
The specific impulse -- force delivered per mass of propellant consumed -- of methane-LOX combustion is generally higher than ...
- 172k
19
votes
Nitrogen trifluoride as a high density oxidiser
It is possibly a jack of all trades and master of none Ignition by J Clark only talks about NF3 as a precursor to making other more exciting fluorine compounds, NF3 itself being mentioned as hard to ...
- 25k
14
votes
How much bigger could Earth be, before rockets wouldn't work?
note: I've accepted an answer 2.5 years ago. This paper was published recently so I thought I would add this supplemental answer since it may be an interesting reference for future readers.
The Space....
- 151k
14
votes
Accepted
Do larger rockets tend to have a better mass ratio due to the square cube law?
It doesn't really work that way, because a tank isn't just a volume; the tank itself is a structural member that needs to support the mass of the material contained inside it (and in most cases the ...
- 8,041
13
votes
Accepted
Could HIBEX propellant be used for amateur rockets?
According to Wikipedia,
HIBEX employed a star-grain "composite modified double-base propellant", known as FDN-80, created from the mixing of ammonium perchlorate, aluminum, and double-base ...
- 172k
13
votes
Accepted
There are better oxidizer than oxygen?
This depends on what "better" is.
But let us talk about fluorine. The main point of using it is that turning your hydrogen into $HF$ gives more energy than getting $H_2O$ for pure hydrogen, that ...
11
votes
Is there a formula for converting a rocket's performance for one orbit to another? E.g. SSO performance to GSO?
No, such a calculation is not possible. The performance to different orbits is determined by the specific parameters of each launcher, e.g. specific impulse of each stage engines, fuel ratio, time of ...
- 15.2k
9
votes
How much bigger could Earth be, before rockets wouldn't work?
Not a planetological exposition in sight so, I'll add my two cents to this rather theoretical discussion.
Amongst exoplanetologists, the consensus has emerged that 1.6 Earth radii and 5 Earth masses ...
9
votes
Benefit of Raptor Engines
I can answer the second question — engines are by and large fuel specific. There's plenty of complicated stuff that goes on in the combustion and the transition to supersonic flow that means you ...
- 6,511
9
votes
Accepted
Does flying two boosters close together affect efficiency?
There is likely minimal effect.
At rocket speeds, there is very little effect of shear stress, the only significant effect is particles hitting the leading surface of the rocket.
Also due to how ...
- 3,442
7
votes
There are better oxidizer than oxygen?
Besides pure oxygen, several other oxidizers in theory have better performance with hydrocarbon fuels, but none of them are used because of stability, toxicity and price issues. But let mention some ...
- 2,341
7
votes
Accepted
Why can Falcon Heavy bring 4.2 times as much mass to Mars than F9, but only 2.7 times as much to LEO?
The final stage of a rocket has to lift not just the payload but also itself. So lets look not at the payload mass alone but at the total mass lifted to the final orbit.
According to http://www....
- 824
6
votes
Why can Falcon Heavy bring 4.2 times as much mass to Mars than F9, but only 2.7 times as much to LEO?
All else being equal (e.g. propellant choice), higher-energy trajectories favor a rocket with more stages.
One thought experiment that can help you understand this is to consider two missions ...
- 10.1k
6
votes
Accepted
What performance specification would be lower for Krypton than for Xenon in Hall effect thrusters?
Hall effect thrusters do not use strong magnetic fields and radio frequency power to heat electrons to high energy for ionization of the gas. Instead they rely on a DC current of electrons accelerated ...
- 134
6
votes
In the context of calculating mass flow rate from thrust and Isp, how would an additional efficiency be defined?
I'd assumed that Isp expresses the axial component of the velocity, so even if there is some transverse flow in the expanding exhaust, that wouldn't have to be accounted for beyond Isp, but is there ...
- 172k
6
votes
What were/are the stingiest and most generous vacuum nozzle? (records for the smallest and largest expansion ratios)
Partial answer to get the ball rolling:
The RL-10B-2 and RL-10C-2-1 variants of the venerable RL10 LH2/LO2 upper stage engine feature an expandable nozzle with a 280:11 area ratio and an amazing 465.5 ...
- 189k
6
votes
Why was Apollo 11 launched in summer?
There were several factors in the launch date
The late John F. Kennedy had promised to go to the moon within the decade. This was a secondary concern, but an important one nevertheless
The failure of ...
- 8,160
6
votes
Could HIBEX propellant be used for amateur rockets?
"Yes", but that would sort of be silly and it would highly depend on where you live, since it may be illegal in your country to mix your own rocket propellant. HIBEX used what is ...
- 6,300
5
votes
Can a lighter rocket lift more than a heavier rocket?
In general, heavier launchers can send more mass to LEO, but as described in this QA, the correlation isn't very strong. Different engine technologies used in modern rockets have different mass/...
- 172k
5
votes
Why was Apollo 11 launched in summer?
The season when the Saturn V launches doesn't matter, especially in Florida where the temperature remains relatively warm year round. The Saturn V was engineered to be very resilient and to withstand ...
- 5,986
5
votes
When would the density Isp product be an important performance metric of a propellant?
When would the density Isp product be an important performance metric of a propellant?
It's always important.
Specific impulse is a measure of impulse provided per mass unit of combusted propellant, ...
- 172k
5
votes
When would the density Isp product be an important performance metric of a propellant?
From the ECAPS page on LMP-103S performance...
The specific impulse is ≥ 6% higher and the propellant density is 24% higher. As a result, the satellite can either be fitted with a smaller tank, or ...
- 8,136
4
votes
Generating plot of LV's performance as a function of the C3 parameter
These plots are best made using a trajectory optimization program like POST or OTIS, which is used to model the LV to some appropriate level of fidelity. Jacks-or-better is engine performance, some ...
- 3,949
4
votes
When would the density Isp product be an important performance metric of a propellant?
While it isn't precisely space exploration per se, John Clark mentions this being important in Ignition for missiles, especially in cases when it is desired to meet a performance goal while having a ...
- 9,517
4
votes
Accepted
What happened to tripropellant rockets?
Al = aluminum is a solid metal, RP1, O2 and H2 are stored as liquids within the tanks of a rocket.
If you know a method to store a liquid preparation of aluminum that may be pumped into a rocket tank ...
- 49.5k
4
votes
Accepted
How could Starship "deep space variants" improve payload performance by "orders of magnitude" (Elon Musk)?
[...] with orbital refilling [...]
This seems to be the part were orders of magnitude can be snuck in .
Refilling the 1,200t propellant tanks of the 120t starship makes it possible to start with a 1,...
3
votes
In the context of calculating mass flow rate from thrust and Isp, how would an additional efficiency be defined?
Russell Borogove has already answered, but I wanted to point out more explicity a few things:
ISP is a derived quantity
You do not need to add any efficiency factor
If the thrust and ISP figures come ...
- 2,113
3
votes
How can I use the Rocket Equation and Staging for a ballistic flight?
Short answer:
Yes, you can use energy balances for this problem and the rocket equation can also be rewritten in a way to include thrust (force), the mass of the fuel and optimal staging.
Long answer
...
- 6,836
3
votes
In the context of calculating mass flow rate from thrust and Isp, how would an additional efficiency be defined?
If I understand correctly that your question is asking about inefficiencies other than those caused by propellants that bypass the main combustion chamber (like gas generator propellants) that aren't ...
- 189k
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