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35 votes
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What was the result of the propellant predictions in the last chapter of "Ignition!"?

Chemical rockets will never have more than 600 seconds specific impulse. Storing free radicals in propellant to defeat this limit is impractical. Validated. Chemical rockets in use top out at 450-460 ...
Russell Borogove's user avatar
20 votes
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What is wrong with hydrazine as a monopropellant?

There are a few reasons why a hydrazine replacement is being looked at: Hydrazine is highly toxic, and carcinogenic so it's dangerous to handle. A leak can put astronauts or technicians at serious ...
GdD's user avatar
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10 votes
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Does peroxide spontaneously decompose when introduced into hot combustion chambers?

HTP will sustain a combustion reaction without a catalyst once ignited, but it's not clear to me if the reaction proceeds quickly and smoothly enough to be a good idea for rocket combustion chambers. ...
Russell Borogove's user avatar
10 votes
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What is the propellant mass for the Soyuz descent module?

The Soyuz Crew Operations Manual says the system holds between 29.6 and 31.4 kg of peroxide. It also has a nice schematic of the system.
Organic Marble's user avatar
8 votes

What is wrong with hydrazine as a monopropellant?

Hydrazine, as for small monopropellant thrusters, has been in use for decades on hundreds of satellites. One model the "1N Monopropellant Hydrazine Thruster" is claimed to be in use in 165 ...
tckosvic's user avatar
  • 2,302
7 votes

Is Landsat-7's propellant resupply port "robot-ready"? (Restore-L mission)

My reading of the Aviation Week article on this seemed to suggest that while Landsat-7 was not designed to be refueled, when they looked at its design, they found a fuel line, they could patch into ...
geoffc's user avatar
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7 votes

Are there any gaseous monopropellants?

All rocket propellants end up in the gas phase and are stored in the liquid or solid phases aboard rockets. Many propellants could easily be stored in the gas phase aboard a rocket, but they are not ...
Slarty's user avatar
  • 9,560
6 votes
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What's up with the lack of subminiature chemical rockets?

Our company (Malin Space Science Systems) is collaborating with Stellar Explorations to develop a very small biprop propulsion system for cubesat missions. There is a definite lack of options in this ...
Terrance Yee's user avatar
  • 2,294
5 votes

Why is the Otto II monopropellant fuel not used in spaceflight applications?

Otto fuel II has a specific impulse of 200 s, which is really low compared to solids at ~250 s, hypergolics at ~250 s and RP-1/LOX at 300 s.
Hobbes's user avatar
  • 128k
5 votes
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Why does New Horizons have ~2 kg of unusable "trapped" hydrazine?

Using Wikipedia: The hydrazine tank of New Horizon has an elastomeric diaphragm separating the liquid from the pressurizing gas helium within zero gravity. There are 16 thrusters with redundant ...
Uwe's user avatar
  • 49k
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, ...
Russell Borogove's user avatar
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 ...
Schwern's user avatar
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5 votes
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How do long range space probes adjust trajectory?

New Horizons used its monopropellant attitude control thrusters for course correction. Because it couldn't make large course changes with the limited fuel available, the choice of targets was severely ...
Russell Borogove's user avatar
5 votes

Why is hydrazine used in arcjet thrusters?

Specific heat, also known as heat capacity, in J/kg K (Joules per kilogram per Kelvin). Water, of all liquids, has the highest specific heat; ammonia and hydrazine have much lower specific heats. Also,...
Jan van Oort's user avatar
5 votes

Helium balloon as a rocket

There are at least two serious issues: Ascending to high altitude is useful in reducing air resistance, but does very little to aid the required orbital velocity of around 7500m/s. Using the gas in a ...
Slarty's user avatar
  • 9,560
4 votes

Is LMP-103S truly a viable replacement for Hydrazine?

I'm the SkySat propulsion lead and have been flying LMP-103S since June 2016 when SkySat-3 launched from India. To answer the question: Yes it is viable and has a number of advantages, mostly the (...
peteza33's user avatar
  • 106
4 votes
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Would (theoretically) metastable solid metallic hydrogen even need an oxidizer?

Yes, the fuel would be used as a monopropellant because as soon as you excite the metallic hydrogen, it will be just H molecules which will quickly bond to each other to Form H2, creating mass amounts ...
user140052's user avatar
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 ...
ikrase's user avatar
  • 8,874
4 votes
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If high-test peroxide is most stable when pure, why are most uses of it in rocketry at lower concentrations?

There are several reasons: Catalyst - In most applications HTP is firstly decomposed to steam an oxygen and than introduced to combustion chamber where spontaneously ignites fuel (usually RP-1). ...
WOW 6EQUJ5's user avatar
  • 2,321
4 votes

Could New Horizons' thrusters' ISP be as low as 157 sec?

Several sources (close to the end) show a table with a rough breakdown of the fuel use. The total amount of fuel of 77 kg was used both for trajectory change and attitude control. The Δv = 242 m/s ...
asdfex's user avatar
  • 15.1k
4 votes
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Do monopropellants have a characteristic length?

It's worthwhile to note that some sources make a distinction between monopropellants based on the mechanic - Barrère et al. (1960) indicate that there are combustion monopropellants such as propyl ...
ecfedele's user avatar
  • 527
4 votes

Deep space mission propellant

The Voyager 1 spacecraft (launched 1977) used hydrazine thrusters, that were tested (and worked) 40 years later in 2017, so that would be one possible propellant.
Eugene Styer's user avatar
  • 1,851
3 votes

Is there a known way a nuclear heating device could move around in the CO$_2$ deposit on Mars?

A nuclear heating device with a mass of around 1000kg wouldn't make a measurable difference on the martian atmosphere in it's total (nuclear) lifetime. If you use MMRTG's, the same power source that ...
Dragongeek's user avatar
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3 votes
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Why would it be "less bad" for hydroxylammonium nitrate monopropellant to freeze than for hydrazine?

I've been unable to find any other reference to the quote in your question, that HAN can be "Allowed to freeze". I suspect what the asker meant was that the satellite could be allowed to operate in ...
Ingolifs's user avatar
  • 6,458
3 votes
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How to calculate catalyst bed geometry (length/radius) for a monopropellant thruster?

Partial answer - First equation: As A McKelvy states in a comment, using Ru to be the universal gas constant of 8.314 J / mol-K will get you the answer given in the paper. Second equation: Given the ...
Organic Marble's user avatar
3 votes
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Multi-stage combustion products?

Chemical reactions in rocket exhaust often occur in multiple stages and usually involve a number of by-products at some concentration. https://www.nature.com/articles/s41467-020-19497-z/figures/1 In ...
Slarty's user avatar
  • 9,560
2 votes

Is Landsat-7's propellant resupply port "robot-ready"? (Restore-L mission)

I would expect that if a satellite had no special design for in-orbit propellant transfer then the initial list of options would centre around the normal ground propellant supply interface, normally ...
Puffin's user avatar
  • 9,644
2 votes
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Density impulse of monopropellant hydrazine?

Well, the density of hydrazine is $1.021 \frac{kg}{L}$, and its $I_{sp}$ is $220 s$ as a mono propellant. (Both values from the Wiki page). That is a total of $224.6 \frac{kg \cdot s}{L}$, using the ...
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