The launch window for Mars missions is only open every 26 months. In this relatively short time frame have to be inserted all the ships into the parking orbit and being refueled as well.
However, there is a fundamental flaw in the in-orbit refueling sequence we know: the ship goes up first and the propellant follows it and as a consequence, the first cargo ship has to wait almost 26 months for its trans-Mars injection burn.
It's a significant problem because in 2 years a lot of R&D happens in all the colonization-related technologies. Just think about the progress that happened since the end of 2018 in the fields of batteries, solar cells, boring machines, robots, drones, 3D-printers... Ideally, these pieces of equipment are being developed and optimized as long as possible and go to the parking orbit lastly.
To do that orbital propellant depots have to be used. Using tanker ships would be obvious but using specialized depot ships would be an even better choice. These propellant depot ships would remain in orbit for decades and serve all the following deep space missions.
Their main differences compared to the tanker ships would be:
* these parts of the ship wouldn't act as body flaps, hence the quotations marks
Starship needs 100 m/s of landing delta-v to land on Earth and about 480 to land on Mars. This corresponds to 6 tons of propellant on Earth and 30 tons of propellant on Mars (for a 100 ton payload and a 120 ton ship). The propellant tank sizes that arise from this propellant requirement matches the actual header tank sizes we have seen within 10%.
This post is an in-depth response to a question posed in this post, a response I provided in the comments, albeit in a much more summarized manner. The question was this: how will starship slow down and land on Mars?
This is a question that gets talked about a lot, and that we have been given a clear answer to, but not something that everybody understands. To answer the question, we begin by looking at starship's approach to Mars.
After launch from Earth, starship will be on an interplanetary trajectory that will put it on a fly-by trajectory past the red planet. Course adjustments during flight will allow it to approach the planet and enter the atmosphere at a prescribed altitude, velocity, and angle. For common transfers to Mars, entry velocities may be on the order of five to six kilometers per second. While the atmosphere of Mars is extremely thin, at these speeds it presents a significant barrier and will do a lot of work to decelerate starship. Starship could do a direct entry into the atmosphere, braking all the way down below orbital velocity in one pass, or it could do many passes, reducing its velocity and lowering its apoapsis (highest point on its orbit) with each pass, much like the MRO did. Musk has stated that direct entry to Mars can be done but multi-pass aerobraking on Earth may be a necessity (higher entry speeds and thicker atmosphere).
No matter the entry method Starship chooses, its trajectory through the atmosphere will be designed so that it first bleeds off its orbital energy going horizontally in the upper atmosphere, before falling into a vertical belly flop until it reaches terminal velocity (velocity where the force of gravity cancels the drag force). From an altitude-versus-range perspective the entry should be somewhat similar to an Apollo reentry:
[Apollo reentry altitude versus range](https://preview.redd.it/iyt6btzg2e761.png?width=474&format=png&auto=we... keep reading on reddit ➡
Hydrolox (liquid hydrogen/oxygen) has been used as a high-efficiency rocket propellant since the 1960s, and is great for sending spacecraft on high-energy trajectories beyond low Earth orbit. Hydrogen and oxygen are available all over the solar system, mostly in the form of water ice. However, it has the drawbacks of being hard to store, needing very low temperatures, and active boil-off mitigation.
This is why SpaceX is using methalox (liquid methane/oxygen) for their Starship launch vehicle, even though it is less efficient in terms of specific impulse/exhaust velocity. It can be more easily stored for long periods of time, and by using the same propellant on both stages, manufacturing and operational costs can be reduced (hydrolox tends to have low density and engines using it have lower thrust, so it is not optimal for first stages). The vehicle is designed for SpaceX's main goal of Mars colonization, and methalox can be produced from the Martian atmosphere and ice through the Sabatier reaction.
However, if your eventual goal is making space habitats from asteroids and moons instead, which is more practical for rocket-based launch vehicles in the near term?
SNels0n made the case for methane here, even though they weren't a "planetary chauvinist": >IMO, methane is a better rocket fuel choice than hydrogen for big space projects. We can store methane. Hydrogen tends to leak out of pretty much everything. Granted 4,400 m/s is bigger than 3,700 m/s but once we reach the "storage depot" stage, specific impulse is no longer the biggest concern.
Finally got a hyper propellant oc and wanted to know what mods should I put on the pgl to maximize damage output?
I’ve noticed a lot of people like both, and there’s a constant debate on which is better, so I was wondering how many people like both, or like to use the Breach Cutter
I've wanted to build liquid rocket engines for a very long time and now is when I will do it. Can anyone help me with how to do it, or recommend a subreddit that might help? Ethanol and Liquid Oxygen if that helps. Thanks!
I used to not know how I felt about Hyper Propellant until today. I had a Gunner on a salvage mission lower my health to about 50% with his mini gun and it kinda pissed me off. Then, when my shield charged, he lowered me down to 10% with his pistol. I just looked at him, shot him once with Hyper Propellant, and that was the end of that. Gg. Rock and Stone.
Can someone explain in simple 5-yo terms what the difference between and explosive and a propellant is?
I get our powders are propellants as they ... propel ... our bullets. But damn if they don’t make an explosion while doing that. Or not?
I read the technical explanation of explosive but was left confused.
https://youtu.be/o_vuqd-ilRg is this vid arca announced isro started its eco friendly propellant Dev. What they missed that ISRO never said they would use water and is using proven tech. Like hydrogen peroxide (valid fuel and works not like ARCA using water heated by batts which is never done and heating by batts is a bad idea.British black arrow also used hydrogen peroxide) for eco friendly prop.and if u think about it SpaceX are also eco friendly using methalox and sebatier process to be carbon neutral ,that’s something ISRO also could do someday .ULA delta 4 heavy is all hydrogen rocket making it the most eco friendly rocket yet.just wanted to post this.(and no offence ,based on ISRO’s track record they will take a LONG time to do eco friendly propellant so ARCA should not jump to conclusions with this.
A recently published paper on nano-additives for performance enhancement in the solid propellants.
Layered magnesium diboride and its derivatives as potential catalytic and energetic additives for tuning the exothermicity of ammonium perchlorate
[ https://www.sciencedirect.com/science/article/abs/pii/S0040603120301830 ]
• Adding 1 wt.% ball-milled MgB2 increases the energy of ammonium perchlorate by 78 %.
• Adding 1 wt.% ball-milled MgB2 reduces the decomposition temperature by ∼73 °C.
The thermal decomposition characteristics of Ammonium perchlorate (AP) significantly affect the combustion performance of the propellant, which in turn determines the degree to which energy can be extracted. To improve the thermal decomposition of AP, fuel additives and burn rate modifiers are incorporated in the fuel.
Generally, metals with a high heat of combustion are used as fuel additives. Some energetic metal fuel additives include Li, Be, B, Si, Al, Mg, Ti, and Zr. Li and Be are not widely used because they are highly toxic and expensive. Aluminum is the most commonly used metal fuel additive because of its wide availability, ease of handling, the high heat of combustion (31.4 MJ/kg), and also more economical.
On the other hand, several burn rate modifiers are added to AP to improve the burning rate of the propellant. The burn rate modifiers or combustion modifiers are classified as catalysts (increase the burning rate) and inhibitors (decrease the burning rate) based on their activity on the combustion performance of the propellant.
Boron is another universal fuel additive in propellants; it exhibits the highest theoretical heat of combustion in terms of both volumetric (135.8MJ/L), and gravimetric (58.5MJ/kg) terms. Yet, scientists are not able to effectively utilize the potential of boron because of the challenges associated with its combustion. The challenge is that upon combustion, boron forms a viscous boron oxide layer on the surface that limits further oxidation of boron.
######Research We then demonstrated that pristine MgB2 (P-MgB2 ) is a potential catalytic and energetic additive for enhancing the thermal decomposition characteristics of AP. To further enhance the activity of P-MgB2, we prepared mechanically activated-MgB2 (MA-MgB2 or micro derivatives) by developing an optimized ball milling recipe.
Seems like a stupid question considering you wouldn't want phase changes in the regerative cooling jacket and store the propellants as a liquid in the propellant tanks. I was mostly interested in whether you could inject two gases and have their streams impinge and if that was an efficient way of combustion. Although I imagine the raptor engine ox-rich and methane-rich propellants are gases when they inject and any fuel in a closed cycle for that matter.