Altaïr's crazy stuff
- Thread starter Altaïr
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I think also you can save more Delta-V using gravity assists more easily with the jovian moon than with mercury. With the Jovian moons VEEGA puts you on jupiter no strings attached, and you can more easily do pingpong with the moons to lower your orbit. Mercury on the other hand requires a double assist from Venus + a powerered assist to hit Mercury's periapsis, you also basically have to land after that (unless you either want to V-leverage and wait 40 years or use ANAIS) which costs more fuel. Mercury also has over twice the gravity of the moons.
I guess I just thought it was harder as I remember when the galilean moons had ridicolously high gravity for no reason (like Ganymede had a gravity of 5.82m/s^2 and an orbital velocity of nearly 1000m/s)
I guess I just thought it was harder as I remember when the galilean moons had ridicolously high gravity for no reason (like Ganymede had a gravity of 5.82m/s^2 and an orbital velocity of nearly 1000m/s)
Altaïr
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1. Happy 7000 posts!
2. Please stop breaking the under pressure record! I was feeling proud of my 11%
2. Please stop breaking the under pressure record! I was feeling proud of my 11%
Honestly 11% is very good, especially with the limited navigation tools the mobile version offers. I recently tried a VEEGA maneuver on mobile, I literally had to re-learn how to proceed, there's no way I could match the efficiency provided by ANAIS...
I made another try on that Mercury challenge, and I broke a new record
View attachment 119313
I needed something epic for my 7000th post.
View attachment 119313
I needed something epic for my 7000th post.
Altaïr you're killing me, now I'll have to do a lunar assist chain into venus assist(s?) into V-leveraging all on mobile when I decide to get a record myself
You'll probab;y spend like a million years V-leveraging lmao
Altaïr
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Altaïr you're killing me, now I'll have to do a lunar assist chain into venus assist(s?) into V-leveraging all on mobile when I decide to get a record myself
16% of remaining fuel on landing. ANAIS is so efficient that it's unfair otherwise, it even allows to complete the challenge without gravity assist.
However I don't think that lunar assists will help much: I didn't try recently, but from my experience the Moon can not provide you enough speed to reach Venus at an appropriate level. Especially that it's not very massive and can't deflect your trajectory by a lot, and as soon as your trajectory exists the Earth SOI you can't do it anymore.
That's correct. Lowering the orbit doesn't just depend on the number of assists, it would be too simple. Two passes are needed because a single pass can't deflect your trajectory enough, but more assists won't help. Once your exit velocity is in the exactly opposed direction of Venus velocity the game is over. Or you have to use the V-leveraging technique, but it will cost fuel. In my opinion it's still better to aim for a low enough orbit while you're making your injection burn from LEO, because at least you benefit from the Oberth effect. V-leveraging is done through deep space maneuvers, which are by definition less efficient.
It is quite the tedious process, but I have used lunar assist chains to gain all of the velocity to get to another planet (minus the moon transfer, so the saving is quite small). Especially without a future planning maneuver system, it takes a ton of time to get back to Earth to do the final assists. You obviously can't spend much fuel at all or you just wasted a bunch of time. I may experiment with calculating orbital resonance for this step. The assists theoretically save something like 80 m/s.
Excuse me Space Stig, I have questions about launchers.
Let's say I have a launcher with three stages, designed to bring 100 tons to LEO. but now I want to use it to launch 90 tons. To avoid excess fuel, it needs to be reduced. How should that be done? Is it just reduce the fuel in one stage, or proportionally on every stage?
I also wondered how this problem is handled in real life rockets. Is the payload is kept close to its designed load limit? If not, how would they reduce the fuel? Or are there other techniques?
Thanks in advance!
Let's say I have a launcher with three stages, designed to bring 100 tons to LEO. but now I want to use it to launch 90 tons. To avoid excess fuel, it needs to be reduced. How should that be done? Is it just reduce the fuel in one stage, or proportionally on every stage?
I also wondered how this problem is handled in real life rockets. Is the payload is kept close to its designed load limit? If not, how would they reduce the fuel? Or are there other techniques?
Thanks in advance!
Altaïr
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Firstly I'll precise that I never worked on mission design. I worked on aerospace long ago, but not about that.
To my knowledge there's no fuel reduction due to variable payload. This is the same rocket, it's designed for a range of payload mass for a particular destination orbit (LEO, polar orbit, GTO...). Not filling completely the tanks could result in a different behaviour: the rocket is lighter but the engines provide the same thrust, so it accelerates stronger, so it's legitimate to wonder how it would behave, when passing Max Q typically. The launcher could also behave differently regarding vibrations, or even the hardware could behave differently. The first Ariane 5 is a good example of that: the inertial central failed because it wasn't designed for such a strong acceleration (the context was different however: the inertial central was the same as for the less powerful Ariane 4, it's been reused for Ariane 5 for saving purposes).
In practice, launchers are adapted by having different configurations (different number of boosters, or different second stage). You couldn't really partially fill a solid rocket booster anyway: it's a mixture that is molded into the casing with a particular shape, and the thrust curve will depend on that shape (the boosters' thrust is not constant over time). Changing the quantity of rocket fuel will change all those parameters. For cryogenic engines, you can stop them whenever you want anyway, and the excess fuel is vented once the mission is over. This is stage passivation, to avoid an explosion that would spread debris in orbit.
Also, on an economical point of view that would make no sense: fuel is only a small fraction of a launcher cost. The most expensive part is by far the engine itself, so saving a little fuel is probably not worth it. This argument loses of its relevance if you consider reusability though: since the engines are reused over several flights and only the fuel remains a consumable, their cost has to be spread over several flights, so the fuel represents a higher cost in proportion.
To my knowledge there's no fuel reduction due to variable payload. This is the same rocket, it's designed for a range of payload mass for a particular destination orbit (LEO, polar orbit, GTO...). Not filling completely the tanks could result in a different behaviour: the rocket is lighter but the engines provide the same thrust, so it accelerates stronger, so it's legitimate to wonder how it would behave, when passing Max Q typically. The launcher could also behave differently regarding vibrations, or even the hardware could behave differently. The first Ariane 5 is a good example of that: the inertial central failed because it wasn't designed for such a strong acceleration (the context was different however: the inertial central was the same as for the less powerful Ariane 4, it's been reused for Ariane 5 for saving purposes).
In practice, launchers are adapted by having different configurations (different number of boosters, or different second stage). You couldn't really partially fill a solid rocket booster anyway: it's a mixture that is molded into the casing with a particular shape, and the thrust curve will depend on that shape (the boosters' thrust is not constant over time). Changing the quantity of rocket fuel will change all those parameters. For cryogenic engines, you can stop them whenever you want anyway, and the excess fuel is vented once the mission is over. This is stage passivation, to avoid an explosion that would spread debris in orbit.
Also, on an economical point of view that would make no sense: fuel is only a small fraction of a launcher cost. The most expensive part is by far the engine itself, so saving a little fuel is probably not worth it. This argument loses of its relevance if you consider reusability though: since the engines are reused over several flights and only the fuel remains a consumable, their cost has to be spread over several flights, so the fuel represents a higher cost in proportion.
It will be a great day when this happens.
It's not a huge concern even with the very successfully reusable and historically cheap Falcon 9, because the brand new second stage required for each flight at a minimum must cost $5-10 million, plus the other costs likely bringing the marginal cost of a normal launch to maybe over $20 million, whilst the fuel cost for each launch for the entire rocket is likely underneath $0.5 million, so not very noticeable
It's not a huge concern even with the very successfully reusable and historically cheap Falcon 9, because the brand new second stage required for each flight at a minimum must cost $5-10 million, plus the other costs likely bringing the marginal cost of a normal launch to maybe over $20 million, whilst the fuel cost for each launch for the entire rocket is likely underneath $0.5 million, so not very noticeable
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It's not a huge concern even with the very successfully reusable and historically cheap Falcon 9, because the brand new second stage required for each flight at a minimum must cost $5-10 million, plus the other costs likely bringing the marginal cost of a normal launch to maybe over $20 million, whilst the fuel cost for each launch for the entire rocket is likely underneath $0.5 million, so not very noticeable
At least in the case of the Falcon 9, it's not necessarily that shocking, because kerosene has the reputation to be cheap. Liquid hydrogen is probably more expensive, because it's hard to make and liquify, but also because of the many constraints that arise from the use of hydrogen. It needs large tanks due to its low density, leaks very easily, is very flamable... and need very complex turbopumps for engines that use them, which makes LOX/LH2 engines even more expensive. Methane is probably much more affordable.
On another topic I'm trying to polish my latest rocket
It's quite hard to make a beautiful design of that large stick
Whoa, turns out just reducing fuel could trigger many concerns. In real life all factors come to play. I had it reversed, it's more like, build a base rocket to launch x tons, then add boosters and / or modify the second stage to carry x+ tons. I think that's more fitting to your answer.
I also didn't know that the engines are more expensive, despite the fuel making around 80-90% of the rocket's mass.
Thank you for the thorough answer, really appreciate it!
Anyway, the Sapphire looks dope!
I also didn't know that the engines are more expensive, despite the fuel making around 80-90% of the rocket's mass.
Thank you for the thorough answer, really appreciate it!
On another topic I'm trying to polish my latest rocket
View attachment 120422
It's quite hard to make a beautiful design of that large stick
View attachment 120422
It's quite hard to make a beautiful design of that large stick
It is really that cheap?
At least in the case of the Falcon 9, it's not necessarily that shocking, because kerosene has the reputation to be cheap. Liquid hydrogen is probably more expensive, because it's hard to make and liquify, but also because of the many constraints that arise from the use of hydrogen. It needs large tanks due to its low density, leaks very easily, is very flamable... and need very complex turbopumps for engines that use them, which makes LOX/LH2 engines even more expensive. Methane is probably much more affordable.
At least in the case of the Falcon 9, it's not necessarily that shocking, because kerosene has the reputation to be cheap. Liquid hydrogen is probably more expensive, because it's hard to make and liquify, but also because of the many constraints that arise from the use of hydrogen. It needs large tanks due to its low density, leaks very easily, is very flamable... and need very complex turbopumps for engines that use them, which makes LOX/LH2 engines even more expensive. Methane is probably much more affordable.
Somehow the Ariane 5 propellent cost is only half the cost of a Falcon 9's oxygen and kerosene, because the Falcon 9 has a much greater mass of those propellents (it's a deceptively large rocket, it seems).
On another topic I'm trying to polish my latest rocket
View attachment 120422
It's quite hard to make a beautiful design of that large stick
View attachment 120422
It's quite hard to make a beautiful design of that large stick
The big A is a nice touch also! Is this still done with fairing pieces, or textures?
The tanks and avionics are also very expensive
Vulcan's... I have to call it tentative because that is what it seems like, tentative plans for SMART reuse are more or less because that's the only possible easy way to reuse parts with a rocket where the first stage goes most of the way to LEO, due to the massive ∆V and reentry heat requirements from returning from that position.
Vulcan's... I have to call it tentative because that is what it seems like, tentative plans for SMART reuse are more or less because that's the only possible easy way to reuse parts with a rocket where the first stage goes most of the way to LEO, due to the massive ∆V and reentry heat requirements from returning from that position.
Altaïr
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I didn't realize... It' true that hydrogen (even in liquid form) is very light (one liter of LH2 weighs 70 grams), which means that even a low mass of it takes a lot of place.
Also the Ariane 5 doesn't only use LOX/LH2 as propellants: unlike the Falcon 9 that fully relies on kerosene, it has two powerful boosters that provide more than 90% of the thrust at lift-off. I tend to forget it, but a single booster of the Ariane 5 is actually heavier than the central core (first stage + second stage and payload included).
In the case of the Ariane 5 it's stored into a ring shaped structure called the equipment bay ("case à équipement" in french):
It makes the junction between the second stage and the payload. It's probably a similar architecture on other launchers since this part must be kept until the end of the flight.
Thanks
The "A" and the complex shapes are made with textures indeed. I'm trash at bp editing, so I use Gimp for those. I'm trash at using Gimp too, but at least Gimp lets me do whatever I want
I don't know by heart the delta-V of each rocket, but the procedure is different for each rocket: the Falcon 9 first stage doesn't use all the propellant and keeps some for its retropropulsive landing. It also has the option to keep even more propellant to return to the launchpad in case the payload is light enough. Otherwise the landing occurs on a sea platform.
In the case of the SMART reuse, the propellants would be fully spent, then only the engines with all the valves, turbopumps and plumbing system would be retrieved. The consequence is that they are used until a later stage of the flight, and so they would reach a higher speed.
Also the Ariane 5 doesn't only use LOX/LH2 as propellants: unlike the Falcon 9 that fully relies on kerosene, it has two powerful boosters that provide more than 90% of the thrust at lift-off. I tend to forget it, but a single booster of the Ariane 5 is actually heavier than the central core (first stage + second stage and payload included).
In the case of the Ariane 5 it's stored into a ring shaped structure called the equipment bay ("case à équipement" in french):
It makes the junction between the second stage and the payload. It's probably a similar architecture on other launchers since this part must be kept until the end of the flight.
I'd say you succeeded.
The big A is a nice touch also! Is this still done with fairing pieces, or textures?
The big A is a nice touch also! Is this still done with fairing pieces, or textures?
The "A" and the complex shapes are made with textures indeed. I'm trash at bp editing, so I use Gimp for those. I'm trash at using Gimp too, but at least Gimp lets me do whatever I want
I don't know by heart the delta-V of each rocket, but the procedure is different for each rocket: the Falcon 9 first stage doesn't use all the propellant and keeps some for its retropropulsive landing. It also has the option to keep even more propellant to return to the launchpad in case the payload is light enough. Otherwise the landing occurs on a sea platform.
In the case of the SMART reuse, the propellants would be fully spent, then only the engines with all the valves, turbopumps and plumbing system would be retrieved. The consequence is that they are used until a later stage of the flight, and so they would reach a higher speed.
Another cause of this is what the rocket is meant for. Falcon 9 is made for LEO launches; Vulcan is optimized for higher energy trajectories. With a higher delta V requirement for most Vulcan missions, the first stage will reach higher velocity too. Vulcan also has boosters that push stage 1 even faster.
Altaïr
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Submission coming soon I'm tired of sfs today
View attachment 120849
I said the lunar assists would help, I didn't know it would take 8 ish. Would not have been possible without using the orbital resonance formulas you've posted Altair.
View attachment 120849
I said the lunar assists would help, I didn't know it would take 8 ish. Would not have been possible without using the orbital resonance formulas you've posted Altair.
Now you have to teach me, I didn't think that you could save that much fuel with lunar assists.