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Eve Suborbital Flight from Sea Level


Wcmille
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I want to calculate the dV I will need for a sea level launch from Eve for sub orbital flight to 100-120km. Roughly how much is required? How much of that dV is due to loss?

My idea is to do a sub orbital rendezvous with another craft that will circularize my orbit. I do not want either craft to stage, so that both craft are fully reusable and can repeat the landing.

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Well, the plan has certainly got guts, I'll give ya that.  :)

There are going to be two challenges here:  one of engineering, the other of piloting.

The engineering challenge is that your orbiting "recovery ship" is going to need to pack a metric crapload of dV, and also have a pretty high TWR.  Orbital velocity at 120 km over Eve is a bit over 3000 m/s.  Your suborbital ship isn't going to be moving very fast, horizontally-- let's say 500 m/s.  So your recovery ship is going to have to decelerate by 2500 m/s to match speeds for rendezvous, and is then going to have to accelerate quickly again by 2500 m/s so that it goes back into orbit instead of falling into eve.  So that's 5000 m/s for the rendezvous maneuver-- and you'd better have a hella big TWR, because you've got very little time to accomplish that.

The piloting challenge is going to be:  you have to establish a rendezvous and dock, given huge dV, very tight spatial constraints, and and extremely tight time budget.  You're going to have to nail it just right:  the timing of the launch from surface, the piloting of both ships.  It's going to be a really impressive challenge.  If you can pull it off, post pics, please!  :)

One thing that might simplify it a bit:  Don't even try to dock them.  Send the kerbal across on EVA.  Several wins, there:

  • In my experience, it's much quicker to EVA a kerbal between two ships than it is to actually dock them.  When your ships are in rendezvous at very-suborbital speed low above Eve's orbit, every second counts.  You really have to complete the crew transfer quickly before both ships fall back into atmosphere.
  • Saves some mass; don't have to carry monopropellant or RCS thrusters.  Also, you don't need a docking port, which may help make your ascent vehicle more streamlined.
  • A kerbal's EVA pack has a huge amount of dV in it, something like 500 m/s or more.  So when your kerbal jumps out of the ascent vehicle, he or she can eke out another few hundred dV for matching speed with the recovery vehicle.  It's a nice little safety margin to have.

As for how much dV you'll need on the ascent vehicle:  That I don't know.  A big part of it depends on the exact design of your ship:  a huge part of the dV on Eve ascent is gravity + aero loss as you slowly climb that first ~20 km or so straight up before you can tip into your gravity turn.  Just how huge is totally dependent on your ship's aerodynamic drag.

If you had to ballpark guesstimate it:  just totally pulling a number out of a hat, I'd suggest "take the total dV for a typical Eve lander to get to orbit, and subtract 2500 m/s".  That's what you'll need to get suborbital.  If you can add a bit more dV to your ascent vehicle so that it's got a bigger horizontal component to its velocity at Ap, then you'll make life a lot easier for yourself:  less dV needed on the recovery vehicle, more time available due to shorter burn times by the recovery vehicle, more time available due to "higher horizontal speed = lower fall rate back into atmosphere".

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33 minutes ago, Wcmille said:

I don't see a stageless craft making it to orbit without assistance at Ap. The full dv for Eve orbit is probably something like 8k, which exceeds what a stageless aerospike can do (about 7k)

Resorting to EVA is an emergency, but not good as a plan. If I'm willing to lose the whole craft in the beginning, I should just use stages.

...Ah, okay, I'd actually missed the "SSTO" bit.  (Might be worth adding the "SSTO" to the thread title-- it makes a huge difference.)

You've really picked a tough row to hoe, then.  That's going to be one hell of an engineering problem, I have no clue how you'd manage that or if it's even possible.

As for wings:  No, that won't help you.  Wings add lift, but no energy.  They're simply an energy sink.  If you fly at, say, a 30 degree climb angle-- whose sine is 0.5-- that means your gravity loss is half as much... but you have to travel twice as far through the atmosphere, which cancels out the benefit.  The only benefit is that you could get by with a lower TWR, which means less dead weight wasted on engines.  But that's about it, and I would guess (though can't mathematically prove) that the extra drag from an airplane-based design would more than offset any TWR benefits.

I'm pretty sure (but would happily be proven wrong, if someone can supply a working counterexample) that the best way to get to orbit on Eve is to just go straight up for the first 20 km or so and then tip over into a classic gravity turn (which requires no lift).  So much of the dV-to-orbit from Eve is waste that happens in atmosphere, rather than actual energy-to-climb or energy-to-accelerate; the atmosphere's such a killer that the best approach is to get above as much of it as possible, as soon as possible, which means a vertical climb.  And keep the ship as streamlined as possible, so that you can do that climb at faster speeds.

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13 minutes ago, Wcmille said:

I want to calculate the dV I will need for a sea level launch from Eve for sub orbital flight to 100-120km. Roughly how much is required? How much of that dV is due to loss?

My idea is to do a sub orbital rendezvous with another craft that will circularize my orbit, allowing for an Eve SSTO with less dV.

You want the SSTO to move at sub-orbital speeds, to rendezvous with something orbiting at 3000+m/s ? I hope i am misunderstanding this, because that is going to be quick docking :P

s = 1/2 * a * t^2
s: shift(distance accelerated-> 100 000m)|  a: acceleration(16.7m/s^2)|  t: time(x)

t = sqrt(s / (a/2))
t = 109.4 seconds

vf = vi + a * t
vf: velocity final|  vi: velocity initial(0m/s)|  a:accel(16.7m/s^2)| t:time(109.4 seconds)
vf =  1827m/s

vf is the dv you need if you could "shoot" you craft upward...not going to happen, so you have to add the amount of seconds that you are thrusting(t = 109.4 + 35) and do the calculation on that. (while you are not yet in the speeding bullet state, you are practically "hovering"...very fast upwards though)
Air resistance is going to add 50-150m/s

From 100km, a small probe could do the last 3000m/s(it will practically be in orbit itself before you can even think about docking to the other craft)...this could get kerbals up and down fairly SSTO like

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I am not completely aware on how KSP handles "multiple crafts in atmo" in 1.1.3, but docking inside the atmosphere was quite tricky before due to the fact that crafts exceeding a 2.5Km distance from the controlled one were simply obliterated by the game.

There are some workarounds but they are hard to pull off even on Kerbin.

I am not so positive this solution is feasible for a Eve craft - not efficient enough.

Take a look at this clip (not mine, but really a masterpiece)

If I misunderstood and you want to dock "suborbital but outside the atmo", I have the same thinking - it is not efficient enough.

Edited by Signo
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Ok, honestly this is so much near "impossible" piloting wise that even if you pull it off it wil be a proof of concept. Nothing you'll even want to reproduce more then once.

It will not be efficient by mass,

I expect the module that takes off from the surface will go straight up, and leave a mobile mining setup nearby. Otherwise it will never function as an ssto.

You will also need a minimum of 6.5-7k delta v on the module outside the atmosphere. To slow down for docking and to get into circular orbit. Assuming your very very efficient and can get both modules at the same time and place.

Youll want extra engine mass on the thingie to get to orbital velocity in record time (meaning a great amount of TWR). Because if the ascent stage falls back into the atmosphere its bye bye.

Youll also want a fuel tank with mining setup on gilly to refuel the orbiting ssto stage around eve. 

Edit: thinking about it. Why even use the term ssto. Its more of a full recovery type of operation.

 

Edited by Vaporized Steel
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Alas,  what you're suggesting is utterly unfeasible,  and though theoretically possible,  is far harder than just launching normally. 

XKCD addressed that in respect to earth :

https://what-if.xkcd.com/58/

 

Basically,  either one of three things can happen :

1: Launch the craft to a cheap suborbital trajectory,  and rendezvous with the orbiting craft.  Which wouldn't be a rendezvous,  but a hypervelocity collision,  destroying both craft. 

2: Keep the launched craft in a suborbital trajectory,  and slow the orbiting craft down, then perform a rendezvous before reentry occurs,  and regain full orbital velocity before reentry occurs.  This would take a massive amount of fuel to achieve,  and would be a delta v achievement greater than a simple launch to orbit,  and a precision rendezvous that NASA likely couldn't pull off. 

3: Keep the rendezvous ship in an orbital trajectory and launch the suborbital craft to orbit.   This is the easiest and most effective way to do it,  and is what most people do anyway.  Have a dedicated lander that returns to a mothership in orbit so the lander only has to have enough delta v to achieve orbit,  and no more. 

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4 hours ago, Snark said:

Well, the plan has certainly got guts, I'll give ya that.  :)

The engineering challenge is that your orbiting "recovery ship" is going to need to pack a metric crapload of dV, pretty high TWR.

You're going to have to nail it just right:  the timing of the launch from surface, the piloting of both ships.  It's going to be a really impressive challenge.  If you can pull it off, post pics, please!  :)

One thing that might simplify it a bit:  Don't even try to dock them.  Send the kerbal across on EVA. 

As for how much dV you'll need on the ascent vehicle:  That I don't know.  A big part of it depends on the exact design of your ship:  a huge part of the dV on Eve ascent is gravity + aero loss as you slowly climb that first ~20 km or so straight up before you can tip into your gravity turn.  Just how huge is totally dependent on your ship's aerodynamic drag.

If you had to ballpark guesstimate it:  just totally pulling a number out of a hat, I'd suggest "take the total dV for a typical Eve lander to get to orbit, and subtract 2500 m/s".  That's what you'll need to get suborbital.

I don't see a stageless craft making it to orbit without assistance at Ap. The full dv for Eve orbit is probably something like 8k, which exceeds what a stageless aerospike can do (about 7k)

Resorting to EVA is an emergency, but not good as a plan. If I'm willing to lose the whole craft in the beginning, I should just use stages.

Suppose it's all possible, the question is at the end: is how much dV do I have to have? Can't figure out if wings help more with lift, or hurt more with drag/weight.

 

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8 hours ago, Snark said:

...Ah, okay, I'd actually missed the "SSTO" bit.  (Might be worth adding the "SSTO" to the thread title-- it makes a huge difference.)

You've really picked a tough row to hoe, then.  That's going to be one hell of an engineering problem, I have no clue how you'd manage that or if it's even possible.

As for wings:  No, that won't help you.  Wings add lift, but no energy.  They're simply an energy sink.  If you fly at, say, a 30 degree climb angle-- whose sine is 0.5-- that means your gravity loss is half as much... but you have to travel twice as far through the atmosphere, which cancels out the benefit.  The only benefit is that you could get by with a lower TWR, which means less dead weight wasted on engines.  But that's about it, and I would guess (though can't mathematically prove) that the extra drag from an airplane-based design would more than offset any TWR benefits.

I'm pretty sure (but would happily be proven wrong, if someone can supply a working counterexample) that the best way to get to orbit on Eve is to just go straight up for the first 20 km or so and then tip over into a classic gravity turn (which requires no lift).  So much of the dV-to-orbit from Eve is waste that happens in atmosphere, rather than actual energy-to-climb or energy-to-accelerate; the atmosphere's such a killer that the best approach is to get above as much of it as possible, as soon as possible, which means a vertical climb.  And keep the ship as streamlined as possible, so that you can do that climb at faster speeds.

Here's where I'm at for the moment. Launched from 1000m, I can put this single kerbal craft up to 335k and 60m/s at Apogee. At that altitude, I should only need ~2600 m/s to make a 90x335 orbit. It was outside of atmo for several minutes. End of burn to apogee was 4 minutes.

The craft is pretty straightforward. Its a mammoth, fuel tanks, a capsule, a big reaction wheel, and a nose cone. No way to dock yet. Just working on the launch. Can't help wondering if there are other designs that yield even more final orbital energy, or what is the ideal mix of altitude and velocity for a given energy.

This craft is about 4240 dV vacuum. In 58 seconds, it's out of fuel, so I still think capture is possible.

Even if these are solvable, how do I land the thing without burning up?

w3wzX0c.png?1

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Well, it's certainly the simplest Eve ascent vehicle I've seen. :)

Docking isn't an issue, I think (that is, if you can work around the dV and piloting/timing constraints); you can stick a couple of docking ports on the side.

As for handling reentry: well, one thing you could do would be for the recovery ship to carry some extra fuel, and transfer it to your ascent vehicle. Doesn't need to be a huge amount, just enough to slow it to just below the overheat-and-kablooie point.

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On ‎7‎/‎6‎/‎2016 at 0:39 AM, Snark said:

Well, it's certainly the simplest Eve ascent vehicle I've seen. :)

Docking isn't an issue, I think (that is, if you can work around the dV and piloting/timing constraints); you can stick a couple of docking ports on the side.

As for handling reentry: well, one thing you could do would be for the recovery ship to carry some extra fuel, and transfer it to your ascent vehicle. Doesn't need to be a huge amount, just enough to slow it to just below the overheat-and-kablooie point.

Here is a variant of the previous lander, at apoapsis. The docking craft, in a 90km x 103.5km orbit, would need ~3700 dV to catch this craft moving at 1335 m/s. This seems hard, but doable.

The wings allow for stability during the gravity turn and control once the mammoth runs out. The exact, best, gravity turn probably matters a lot. I'm also curious if I could still make this design stronger somehow and give myself and even further margin.

One idea for docking that I have is to remove two of the six aerodynamic domes above the aerospike stacks and replace them with shielded docking ports. Then you'd multi-dock the lander's nose into the rear of the capture vehicle, and use the lander's engines for the final circularization burn. I have some concerns about the stability of the craft, and this might require redesign.

A problem with docking ports on the side of the lander (really, anywhere) is stability under high-thrust. Once connected, the two craft will be very interested in the maximum possible thrust.

I don't understand your final point about re-entry. At present, I am simply using HyperEdit to put the craft on Eve's surface to see if I can even get it off the planet. Once that works, if I can get comfortable enough to carry a little more weight, perhaps I can use wings and chutes to help.

DXjOyCb.png?1

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16 hours ago, Wcmille said:

A problem with docking ports on the side of the lander (really, anywhere) is stability under high-thrust. Once connected, the two craft will be very interested in the maximum possible thrust.

I don't understand your final point about re-entry. At present, I am simply using HyperEdit to put the craft on Eve's surface to see if I can even get it off the planet. Once that works, if I can get comfortable enough to carry a little more weight, perhaps I can use wings and chutes to help.

Ahhh, okay, now it clears up.  I hadn't grasped that your intent was to "capture" the entire ascent vehicle and pull it to orbit.  I'd been thinking that all you need is to rendezvous with it so you can transfer the crew, and then it would just undock and fall back to Eve as the recovery ship then accelerates to orbital speed.

I'm curious, how's your TWR on takeoff?  Do you actually need the six aerospikes, or could you put inverted nosecones on the bottoms of those tanks for better aerodynamics?

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@Snark,

Takeoff TWR turns out to be an extremely important factor, as you alluded to. Some craft designs with higher TWR with LOWER dV have outperformed higher dV craft (in terms of final specific orbital energy) because they don't let the lower atmo eat off all the dV. An all aerospike design is much lighter, with much more dV, but will barely break atmo. I cannot find a vector design that outperforms the mammoth, the small difference in TWR appears to matter.

My memory is that my current best design has a vacuum TWR of about 2.

In an all-mammoth design (my initial design), I'd probably just remove the side tanks entirely. The problem with the mammoth after about 15km is that it's not earning it's pay very well. You must throttle back, or you burn up, so this design actually lets the mammoth burn out at the time the aerospikes hit TWR 1.0. You don't burn up, and then you get the better  dV. More aerospikes lets you hit the TWR sooner, but engines that aren't firing are dead weight, so I fully believe better designs are still unknown to me.

I'd like to "engineer" the correct craft, but the aerodynamics and atmo effects dominate the behavior, putting the math beyond me.

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So, yea, as linked:

Suborbital doesn't mean straight up, more horizontal is more efficient... but gives you less time for the rendevous.

It would be more efficient to let the ascent craft fall back to eve and just transfer the kerbal (with any science). With a high enough TWR you could re-establish orbit for the orbiter, and switch back to the now empty "lander" which should presumably have an easy time reentering and landing. The problem is refueling the lander/ascent vehicle, and getting it back to a suitable launch point.

Having the lander/ascender pack its own ISRU is going to kill the ascent... so you'd need a 2nd mobile ISRU and refeuler to go out and refeul the ascent/lander vehicle... which means you must ensure your ascent/lander vehicle lands where there is ore (you'll also need ore close to the highest mountain on eve)

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6 hours ago, KerikBalm said:

So, yea, as linked:

Suborbital doesn't mean straight up, more horizontal is more efficient... but gives you less time for the rendevous.

It would be more efficient to let the ascent craft fall back to eve and just transfer the kerbal (with any science). With a high enough TWR you could re-establish orbit for the orbiter, and switch back to the now empty "lander" which should presumably have an easy time reentering and landing. The problem is refueling the lander/ascent vehicle, and getting it back to a suitable launch point.

Having the lander/ascender pack its own ISRU is going to kill the ascent... so you'd need a 2nd mobile ISRU and refeuler to go out and refeul the ascent/lander vehicle... which means you must ensure your ascent/lander vehicle lands where there is ore (you'll also need ore close to the highest mountain on eve)

There is an optimal altitude based on time out of atmosphere and rendezvous speed.  Going higher reduces the orbital velocity. Going lower wastes less energy from the lander, as you say. The orbiter should have its PE at 90k, so that it is moving as slow as possible at rendezvous. Several hundred dV can be saved this way, since the orbiter must both slow down and speed up.

If you do not capture the lander in orbit, you have all the limitations you describe. An ideal solution fully captures the lander.

The main problem I did not solve in my solution was re-entry. A craft loaded with fuel has a high ballistics coefficient, and burns up easily.

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If you do not capture the lander in orbit, you have all the limitations you describe. An ideal solution fully captures the lander.

Well, that depends on your definition of ideal. Fully capturing the lander is inefficient, as that requires accelerating extra dry mass to orbital velocity. Thus by no accelerating the lander to orbit you should see significant dV and TWR gains for the orbiter.

However, its probably worth it because the ground handling and moving the lander back to the launch location would be a major annoyance. In a hypothetical scenario where any place on the surface is as good as any other place (ore, altitude), then maybe you wouldn't want to accelerate the lander to orbit.

On the other hand, if there is no ore/ISRU on the surface, then you certainly want to capture the lander so you can refuel it from a tanker getting its fuel from somewhere else.

Also, if you want to bring new kerbals to eve, and back up, its probably easier. One could send all the kerbals on the surface of eve back up... and any new kerbal will have no way to get down to the surface... except with another suborbital rendevous.

-or you could try crew transfers during the first suborbital rendevouz- not only requiring you to dock, transfer a kerbal from the lander to the orbiter... but then also transfer a kerbal from the orbiter to the lander

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The orbiter should have its PE at 90k

If you want to get exploity, you can go lower. As long as the PE is high enough that it won't despawn while on rails, you can have it orbitin with its PE well within the atmosphere as long as you don't make it the active vessel/get it within the "physics bubble" of an active vessel so that atmo drag calculations get done on it

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While I do think this is impossible to actually pull off with human flying I had a thought on how the maneuvering could be handled much faster:


Docking is slow--so don't dock.  The ascent vehicle has a claw on the nose and is flying tail-first at rendezvous.  It has major league RCS because it doesn't have time to maneuver carefully.

The two vehicle has a plate (but nothing like solid) of girders on the front and it's engines are widely spaced.  Adjust the thrust of the engines so it burns properly despite the certainly off-centered mass of the ascent vehicle.

If MechJeb were programmed to do this I think it could pull it off.  I doubt a human could, though.

You're burning a huge amount of fuel in the capture but a tanker could bring more in from Gilly.

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