Altaïr's crazy stuff

[Dahzito]

1. TtTOtW very much rings a bell
2. At least it's more magnificent than the Phalanx Ambition SSTO.
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I did that:

Don't forget to say that it's inspired in my SSTO.

Also it's a good start for Altäir, in my opinion, on it's path to construct Space Shuttles

 

[Lemniscate Biscuit]

Don't forget to say that it's inspired in my SSTO. View attachment 112191 View attachment 112192 View attachment 112193

Also it's a good start for Altäir, in my opinion, on it's path to construct Space Shuttles

That's true Dahzito

 

[Altaïr]

Taken from a menace:
"This dont look like a shuttle disqualify him!"

Ah, a quote from a very respectable man...

Also it's a good start for Altäir, in my opinion, on it's path to construct Space Shuttles

Thanks! I feel like it will be a long road though.

 

[Marmilo]

Ok, I've tried something I've never attempted until now: building a shuttle!

Here is what I came with:
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Isn't it magnificent?

Spoiler

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Ok, it looks like a dead fish. What immediately came to my mind was that this shuttle was truly the trashiest of the World.
"Truly the Trashiest Of the World" sounded like a good qualification for that pile of junk, so I chose to name it officially the "TtTOtW". I'm sure that everybody will find this unpronunceable name very appropriate.

By the way, the fact that it has a booster leaves no doubt about the fact that it qualifies as a shuttle, so at least I'm happy with that.

Ok, let's make it fly!
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The TtTOtW happens to be hard to control and very unstable. Reaching orbit with this unpractical launcher requires a lot of training. And a huge pain resistance. And chance.

Now that I'm in orbit, the TtTOtW can release its payload:
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You'll notice the huge cargo capacity of the TtTOtW, it only requires 143 TtTOtW launches to bring 1 kton to orbit.

Then it's time to reenter:
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Have a look at how the TtTOtW glides with majesty over the atmosphere at hypersonic speeds, piercing through the deadly plasma waves as if the danger didn't exist:
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Isn't that how a shuttle is supposed to reenter?

Then finally, the landing:
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The dead fish is back!
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Except that it looks even more dead than before because of the burn marks...

Ok, time to leave that ship, mission accomplished for the... Hey, wow!
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Crap, the engines suddenly reignited, the TtTOtW is now uncontrollable!

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Oh well, maybe it's better like that to be honest.
I know somebody that officially wants to kill me...

Altair, respectfully... What the fuck

 

[Lemniscate Biscuit]

Altair, respectfully... What the fuck

This made me laugh soo hard.

 

[Altaïr]

Altair, respectfully... What the fuck

I can't say I didn't expect such reaction

 

[Noor Nehan]

blazer would surely and respectfully kill tickle Altair if he saw the shuttle

 

[Marmilo]

I can't say I didn't expect such reaction

Just noticed the white text lol

 

[Axiom]

Then once in solar orbit I lower my perihelion to cross Mercury's orbit with an angle

Are gravity assists more powerful if you enter at an angle?

 

[Altaïr]

Are gravity assists more powerful if you enter at an angle?

Technically yes, but it's not just that: if I didn't do that the next gravity assist would lower my orbit instead of raising it. And it's something I have to repeat after each gravity assist because it also raises my periapsis. This is a technique called V-infinity leveraging.

 

[Axiom]

Technically yes, but it's not just that: if I didn't do that the next gravity assist would lower my orbit instead of raising it. And it's something I have to repeat after each gravity assist because it also raises my periapsis. This is a technique called V-infinity leveraging.

Why would it lower your orbit? doesn't it depend on which side you do the assist on?

 

[Altaïr]

Why would it lower your orbit? doesn't it depend on which side you do the assist on?

It's actually a simplification, but that's actually enough to understand what happens in that case. The problem if you don't lower your periapsis is that you'll find yourself in a situation like this:

On this drawing, the planet is moving to the right, your craft comes from the left. You can notice that no matter which side you choose, your trajectory will be deflected such that the craft passes in front of the planet, so the result in both cases is that the ship will slow down.
Lowering the periapsis allows to encounter the planet from a different angle, so you will have the opportunity to speed up.

 

[Axiom]

It's actually a simplification, but that's actually enough to understand what happens in that case. The problem if you don't lower your periapsis is that you'll find yourself in a situation like this:
View attachment 118621
On this drawing, the planet is moving to the right, your craft comes from the left. You can notice that no matter which side you choose, your trajectory will be deflected such that the craft passes in front of the planet, so the result in both cases is that the ship will slow down.
Lowering the periapsis allows to encounter the planet from a different angle, so you will have the opportunity to speed up.

Ok, does that also happen when you're coming into mercury and trying to slow down?

I want to get better at mercury missions

 

[Altaïr]

Ok, does that also happen when you're coming into mercury and trying to slow down?

I want to get better at mercury missions

The phenomenon is exactly the same, but the situation is reversed: you do try to slow down in this case. However, it's still better to lower a little your periapsis below Mercury because an encounter in the situation above produces a really small effect. Just a little.

Here is how I proceed. Here I'm waiting for a Mercury encounter:


I've made sure that my trajectory crosses Mercury's orbit in 2 distinct points:

Something very important to be aware of is that an encounter won't provide the same result on both nodes. Here the most efficient node will be the green one, when the craft is on an ascending trajectory. This is because during the fly-by, Mercury will continue its movement around the Sun, and during this time, the direction of its velocity vector will slightly vary. The angle by which it varied will be added or substracted to the angle by how much is deflected your craft. Of course, you'd prefer it to be added for maximal efficiency. This will happen on the node I showed you.

Now this is the encounter at that node:

On the last pic, you can clearly see how the craft trajectory will be deflected: anticlockwise. As Mercury keeps moving around the Sun, its velocity vector rotates clockwise. As you want to slow down your intention is to break up as much as possible the alignment of your velocity and Mercury's velocity, so it's better to make those 2 effects add up to eachother.

Then upon exit, your apoapsis has been lowered as expected...

But your periapsis has been lowered aswell:

To counter that effect, just time-warp to the apohelion, and burn prograde to raise your periapsis again:

This maneuver is what will allow to reduce the speed difference on the next encounter.
If your intention is to perform another gravity assist, as before it's better to let your trajectory cross Mercury's orbit in 2 separate points. But if you plan your orbit insertion on the next encounter, then make your trajectory tangent to lower the encounter speed as much as possible.

 

[Axiom]

Ok that makes sense, thanks!

To counter that effect, just time-warp to the apohelion, and burn prograde to raise your periapsis again:

Wouldn't that make the orbit not resonant? I'm relying on getting resonant orbits to chain encounters without having to wait a million years

 

[Altaïr]

Ok that makes sense, thanks!

Wouldn't that make the orbit not resonant? I'm relying on getting resonant orbits to chain encounters without having to wait a million years

Oh yeah, that would break the resonance. In this case it's probably better to keep your orbit resonant and only make said correction after your last gravity assist and prior to your encounter. You'll break the resonance only once that way.

 

[Axiom]

Oh yeah, that would break the resonance. In this case it's probably better to keep your orbit resonant and only make said correction after your last gravity assist and prior to your encounter. You'll break the resonance only once that way.

That makes sense, I would be able to do this if I had ANAIS. I would do the V-leveraging and then burn at periapsis to get the resonance back

 

[floatingfuel]

May I ask a few extra questions?

1. Should one do the V-infinity leveraging everytime after encounter?
2. Which is better, V-infinity or powered assist?

Thanks

 

[Astro826]

May I ask a few extra questions?

1. Should one do the V-infinity leveraging everytime after encounter?
2. Which is better, V-infinity or powered assist?

Thanks

A powered in this case is the same as just doing part of the escape burn but at a way later time. As for V-leveraging every time, I would say yes, you're not getting anything out of a repeat flyby of Mercury if you didn't lower your periapsis

 

[Altaïr]

May I ask a few extra questions?

1. Should one do the V-infinity leveraging everytime after encounter?
2. Which is better, V-infinity or powered assist?

Thanks

For the first one, I would say not necessarily every time, especially if you aim for a resonant orbit and you don't want to break the resonance. You can skip the maneuver so you won't have to go through the painful process of getting a random encounter every time, but you'll have to do it at some point.

As for the second question, I would say that it depends on the situation, though I found that V-infinity leveraging could save more fuel in practice. A powered assist is used in different situations and still proves to be useful though. It is typically used when a gravity assist is slightly not powerful enough for what you want to do. For example, if a Mercury assist doesn't lower your trajectory enough (because you'd like to aim for a resonant orbit to ease your next encounter for example), you can make a powered assist to compensate, at the price of fuel obviously. The burn is typically made when you're close to the planet you're flying by, so you benefit from the Oberth effect. This is what makes this maneuver efficient. It happens that I do it, but mostly for small corrections: if the powered assist does most of the job it kinda ruins the principle of relying on gravity assists to save fuel.

 

[Astro826]

For the first one, I would say not necessarily every time, especially if you aim for a resonant orbit and you don't want to break the resonance. You can skip the maneuver so you won't have to go through the painful process of getting a random encounter every time, but you'll have to do it at some point.

As for the second question, I would say that it depends on the situation, though I found that V-infinity leveraging could save more fuel in practice. A powered assist is used in different situations and still proves to be useful though. It is typically used when a gravity assist is slightly not powerful enough for what you want to do. For example, if a Mercury assist doesn't lower your trajectory enough (because you'd like to aim for a resonant orbit to ease your next encounter for example), you can make a powered assist to compensate, at the price of fuel obviously. The burn is typically made when you're close to the planet you're flying by, so you benefit from the Oberth effect. This is what makes this maneuver efficient. It happens that I do it, but mostly for small corrections: if the powered assist does most of the job it kinda ruins the principle of relying on gravity assists to save fuel.

For the first point, if your goal is V-leveraging, I don't see why you shouldn't do it. If you're not going to do the deep space maneuver to get the benefit of V-leveraging, the assist isn't doing much for you. Why calculate an encounter with the goal of V-leveraging if you're not making use of it? I think one way you could set up a resonance that allows V-leveraging is to get an orbit that is very slightly out of sinc, so on your last orbit you do the deep space burn that gets on an encounter.

When leaving Mercury, using a powered flyby to gain the velocity to reach Venus is (theoretically) the same as a normal escape burn, you're at the same point in an orbit(at Mercury) and getting the same oberth effect as a normal escape burn. So that's not a very effective use. But if you need a powered assist to get a decent resonance for your next V-leveraging flyby as you said, it is definitely a good use case.

 

[Altaïr]

For the first point, if your goal is V-leveraging, I don't see why you shouldn't do it. If you're not going to do the deep space maneuver to get the benefit of V-leveraging, the assist isn't doing much for you. Why calculate an encounter with the goal of V-leveraging if you're not making use of it?

You're totally right, and that's how I usually proceed. But in practice it's hard to keep the orbit resonant while taking into account the deep space maneuver. As the procedure needs to apply it several times (like the Messenger probe that did it 3 times), you can skip the DSM once, and after the next fly-by perform a more important DSM to compensate. I'm not sure that this is strictly equivalent in terms of ΔV however. It just makes things a little less painful by allowing you to skip once the random encounter process.

With ANAIS it's different: I can make my DSM once at the apohelion, then once I'm back at the perihelion resynchronize my orbit with Mercury by aiming for an encounter after a large number of turns. A correction made several turns in advance will be way cheaper, so it's viable in practice.

When leaving Mercury, using a powered flyby to gain the velocity to reach Venus is (theoretically) the same as a normal escape burn, you're at the same point in an orbit(at Mercury) and getting the same oberth effect as a normal escape burn. So that's not a very effective use.

Also agreed. In this case I was more thinking about the case of an insertion around Mercury, where your powered fly-by would slow you down, and would be equivalent to make part of your insertion burn at that moment. But that's basically the situation you describe in reverse. And yes, you'd better have a good reason to do this in practice.

 

[Axiom]

For the first point, if your goal is V-leveraging, I don't see why you shouldn't do it. If you're not going to do the deep space maneuver to get the benefit of V-leveraging, the assist isn't doing much for you.

I'm pretty sure that you can get things out of gravity assists without V-leveraging, like look at a Jupiter assist for example, you can greatly speed uo your craft without having to change anything

I think one way you could set up a resonance that allows V-leveraging is to get an orbit that is very slightly out of sinc, so on your last orbit you do the deep space burn that gets on an encounter.

That's very difficult to do without ANAIS as you may over/undershoot your encounter and still be off. This would be viable with the closest approach line but we don't have it

When leaving Mercury, using a powered flyby to gain the velocity to reach Venus is (theoretically) the same as a normal escape burn, you're at the same point in an orbit(at Mercury) and getting the same oberth effect as a normal escape burn. So that's not a very effective use. But if you need a powered assist to get a decent resonance for your next V-leveraging flyby as you said, it is definitely a good use case.

Assuming you mean leaving Mercury, getting a resonant orbit and then doing a powered flyby, I don't think so as you'll be going faster (more oberth effect) and have the benefit of a mercury gravity assist

 

[Astro826]

I'm pretty sure that you can get things out of gravity assists without V-leveraging, like look at a Jupiter assist for example, you can greatly speed uo your craft without having to change anything

A gravity assist certainly does have benefits, but a pure gravity assist does not change your relative velocity to the planet, it changes your relative direction. It aligns or misaligns your velocities, which changes your orbit around the sun. But you're still moving past Mercury at the same speed, so it isn't making a big difference when velocity relative to Mercury is what you need to change to capture or reach venus to leave. That's where the deep space burn of V-leveraging comes in, a relatively cheap burn can significantly change your relative velocity on the next flyby.

Assuming you mean leaving Mercury, getting a resonant orbit and then doing a powered flyby, I don't think so as you'll be going faster (more oberth effect) and have the benefit of a mercury gravity assist

If you leave Mercury at 100 m/s (for example) and don't change anything between the encounters, you will encounter Mercury still at 100 m/s, so your velocity will be the same, thus no change to oberth effect. It could be useful I guess if you have a very low twr, as it's a lot like splitting up an escape into separate passes.

 

[Axiom]

A gravity assist certainly does have benefits, but a pure gravity assist does not change your relative velocity to the planet, it changes your relative direction. It aligns or misaligns your velocities, which changes your orbit around the sun. But you're still moving past Mercury at the same speed, so it isn't making a big difference when velocity relative to Mercury is what you need to change to capture or reach venus to leave. That's where the deep space burn of V-leveraging comes in, a relatively cheap burn can significantly change your relative velocity on the next flyby.

Actually I think you're right now, just checked the sceenshots for my mercury return mission and they were at around the same speed, If I V-Leveraged I would have gotten a slower speed but I can't do that while keeping the orbit resonant (yet another reason why I want ANAIS)

Fun Fact: in the challenges tab a Mercury return is rated as 'extreme', while any of the jovian moons' return is only rated as 'hard', that's odd because I always thought that the jovian moons were harder