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davidpsummers

Nuclear Space Plane for Eve. Possible?

Question

I've been trying to make an all nuclear space plane for Eve.  The problem is that I don't have enough thrust.  My most recent attempt (see below) could, even if boosted into low alt. flight by drop engines (not shown), not quite maintain speed at level flight.

Now it is intended for Eve where, I suspect, given the thick atmosphere, I could replace wings (I was trying to reduce the stall speed) with much smaller ones.  Is there any chance that will be enough to reach stall speed on taxis and that I could get into orbit before I run out of fuel?

https://www.dropbox.com/s/25z981pqdzdiovi/Nuclear Space Plane.png?dl=0

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Not a chance.  The issue is pressure, and the Nerv hits zero thrust at two atmospheres, which is less pressure than at any point on Eve's surface.  Actually, it's zero Isp, but you're still not going to space today.  There may be mods that offer nuclear thermal jets which will get you to orbit (or at least high enough that the Nervs work), but there is no stock nuclear solution.  It is possible to use a Mammoth (and by extension, Vectors) on a flying fuel tank to get from surface to orbit with one stage, but even that has minimum altitude that's a few kilometres above sea level.  I don't know whether it's been tested, but it might be possible to do it with a Mastodon from Making History, as well.  Either way, you need a lot of punch and either a lot of surface efficiency or else a lot of stages.

On the other hand, if you are only interested in flying at Eve, not actually landing there, then it could possibly be made to work.  Of course, that negates the advantage of the thick atmosphere, so you're better off keeping the wings you have or otherwise configuring for high-altitude flight.  'Flying Low' begins at 22 kilometres, so you need to get that low for the science, but the pressure there is somewhere between one-quarter and one-third of an atmosphere.  I don't know whether you can come back up from that on nuclear power alone.

Edited by Zhetaan

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You're talking about taking off from the surface of Eve with a NERV-powered plane?  Nope, not even close to possible. 

You can use the new stock delta-v tools to check this out - plop down a NERV, select Eve and play around with different elevations.  I tried 10km, which is significantly higher than Eve's highest mountain.  At that elevation, the NERV gets less than 4kN of thrust, and and ISP of 34.  I can't imagine it's possible to get a plane to work in that environment, especially with the additional gravity.

To add one more data point, at 9km altitude (still higher than the highest mountain), the NERV produces zero thrust. 

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18 hours ago, Aegolius13 said:

You're talking about taking off from the surface of Eve with a NERV-powered plane?  Nope, not even close to possible. 

 

 

9 hours ago, Zhetaan said:

Not a chance.

 

To all you doubters:

NOTE: Matt does not take off and get back to Kerbin with this plane... Although he does get there. So... 

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@Duck McFuddle Always assume the OP avoids mods or is new to KSP. ;) If either condition is true then the answer remains no. Now, obviously, if the OP knew KSP well, they would know that the NERV is not even good for planes on Kerbin.

11 hours ago, Zhetaan said:

Not a chance.  The issue is pressure, and the Nerv hits zero thrust at two atmospheres, which is less pressure than at any point on Eve's surface.  Actually, it's zero Isp, but you're still not going to space today.  There may be mods that offer nuclear thermal jets which will get you to orbit (or at least high enough that the Nervs work), but there is no stock nuclear solution.

You quoted the right person for your answer, but the wrong part of their post. ;)

In my experience, though, nuclear turbojets cannot get you to space. Neither the Atomic Age jet engine (in your linked video) nor the equivalents in Mk2 and Mk3 Stockalike Expansion are even Whiplash-alike in performance. I think they are Panther-alike at best.

Edited by JadeOfMaar

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18 hours ago, Duck McFuddle said:

To all you doubters:

Hence my initial clarification about using the NERV specifically, and not a mod-derived nuclear engine.  

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It could be an LFO-powered staged spaceplane, too, I suppose. It doesn't necessarily need parachutes.

 

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1 hour ago, davidpsummers said:

So the only real option is drop a stages rocket onto the surface with parachutes?

Essentially, yes.

Theoretically, there are any number of possible solutions. Practically, though, you need a ship with a minimum vacuum dV of about 8k m/s. And of that, the first 2k m/s or so dV has to be provided by one of only 3 engines that you need to get up to an altitude of about 20km or so: the Aerospike, the Vector or the Mammoth. No other engines provide enough thrust at Eve sea level. If you were to start on a mountain, you might be able to use a Mainsail, Twin Boar, maybe even Thuds on your first stage.

Once you get up to about 15 km, atmospheric pressure is about equal to sea level on Kerbin, so you can use any combination of engines that would work there. The trouble is that for efficiency, you really should be continuing to use whatever engines got you up there to start with, or at least a couple of them. Your ship is either truly massive and Mammoth-based, or a cluster of 1.25m cores propelled by a mix of Vectors/Aerospikes.
And to get out of the thick lower atmosphere, you need to stay as sleek as possible. Adding wings is probably not a great idea...

To get all that down to the surface to start with, you again have any number of options. You can do a powered slow-ish entry into the atmosphere then refuel using drills and ISRU. You might be able to make it down on wings.
However, you really need a way to ditch excess weight and drag before trying to make it back up out of the atmosphere. And so, again, your options are limited. I find it hard to imagine a ship that would let you glide and land on wings, and maybe even take off on wings, but let you ditch the wings so you can power out of the lower atmosphere.
Similarly, trying to carry drills and ISRU back up to orbit is going to be a huge handicap, so you need to ditch them... and so it would be simpler to start by just landing with a spare fuel tank rather than spending all that effort with mining equipment...

So essentially that takes us back to "dropping everything with parachutes"...

Edited by Plusck

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7 hours ago, davidpsummers said:

So the only real option is drop a stages rocket onto the surface with parachutes?

 

6 hours ago, bewing said:

It could be an LFO-powered staged spaceplane, too, I suppose. It doesn't necessarily need parachutes.

 

Also worth noting that you can do a spaceplane without making it an SSTO.  It's possible to design something that starts like a plane, and then stages off most/all of the airplane stuff (along with some engines and fuel, presumably) partway through the ascent), leaving behind something that's more like a rocket.  But I've never tried that with Eve so can't say how well it might work there.  

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On 3/4/2019 at 2:50 PM, Plusck said:

Practically, though, you need a ship with a minimum vacuum dV of about 8k m/s

The delta-V map says 6000?  Is that not likely to do it?

On 3/4/2019 at 2:50 PM, Plusck said:

And of that, the first 2k m/s or so dV has to be provided by one of only 3 engines that you need to get up to an altitude of about 20km or so: the Aerospike, the Vector or the Mammoth.

How about the SRBs?

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1 hour ago, davidpsummers said:

How about the SRBs?

Looks like the answer is no.

 

Any suggestions on taking a long thin rocket and keeping it upright when it touches down?  I assume plenty of parachutes will make it gentle and help.

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2 hours ago, davidpsummers said:

The delta-V map says 6000?  Is that not likely to do it?

I don't know which delta-V map you're using, but 8,000 m/s is the correct figure.  It's possible that you're getting 6,000 from a map that assumes you're taking off from a mountain.

2 hours ago, davidpsummers said:

How about the SRBs?

SRBs are not a good choice.  The Thumper and the Kickback will both light at Eve sea level but they won't produce very much useful thrust.

49 minutes ago, davidpsummers said:

Any suggestions on taking a long thin rocket and keeping it upright when it touches down?  I assume plenty of parachutes will make it gentle and help.

Parachutes work exceptionally well on Eve; you actually don't need very many compared to what you would want on Kerbin.  However, keeping the rocket upright is more a function of two things:  the arrangement of the parachutes with respect to your centre of mass and the landing zone.  The first is not an issue if you build symmetrically, and the second is not an issue if you land somewhere flat and with negligible horizontal velocity.

Assuming you can either control your descent speed or shield well, there are other tricks, too.  For example, you can have splayed landing 'legs' made of I-beams with landing gear on the ends that will give you a very broad base.  Mount the legs on decouplers and you don't have to take them back up.  Think of them as a not-so-big, not-so-fancy rocket holder and you'll be in good stead.  Or you could try the more traditional approach of having your landing gear on out-rider fuel tanks.  You can use girder segments turned horizontally to make impromptu landing skids.  Of course, for any of these, you'll need to be careful that your rocket doesn't flip on descent, but in fairness, that's an issue at any time that you make a landing on an atmospheric body with more than a pod.

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18 hours ago, davidpsummers said:

The delta-V map says 6000?  Is that not likely to do it?

How about the SRBs?

Thanks to @Zhetaan for responding to this.

I'd just add that this is 8k vacuum dV we're talking about, and assuming that your choice of engine is an efficient one.

Orbital velocity in low Eve orbit is not all that high. I seem to remember it's something like 3500 m/s.
Therefore, assuming you "lose" about 2k m/s dV just getting out of the lower atmosphere, and then lose another 1k m/s completing your gravity turn much like you would on Kerbin, then your theoretical dV cost is actually more like 6.5k m/s.

However, there is no way to calculate that in stock or with mods like KER, since your ISP is changing dramatically all the way up. You can make a rough guess, for example by setting altitude to 1km and checking the dV numbers for your first stage, then setting altitude at 20km and checking the second stage, etc. You might end up with a number of around 6k dV... or not...

Edited by Plusck

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You can get to Eve orbit from SL with around 5500 dV (vac) if your craft is really, really low-drag and you make the best engine choices. 

Edited by Foxster

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Just for giggles, here's a nuke-upper-stage not-spaceplane that'll easily make Eve orbit from SL...

MeTsnO5.png

Edited by Foxster

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This is an easy question. Getting to Eve with an all Nuclear (and Rapier I presume)-powered SSTO is totally a blue run.Getting off Eve with an all nuclear-powered SSTO is utterly impossible.

14 hours ago, Foxster said:

Just for giggles, here's a nuke-upper-stage not-spaceplane that'll easily make Eve orbit from SL...

My $0.02 would be that as more-or-less payload to get you wherever you might be going after you make orbit, nukes are as good on Eve as anywhere else. But if you're counting on them to substantially help you in the actual process of getting to orbit, you're asking quite a bit of them.

Edited by herbal space program

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15 hours ago, Foxster said:

You can get to Eve orbit from SL with around 5500 dV (vac) if your craft is really, really low-drag and you make the best engine choices. 

My current record with a 5m craft from SL is 5,202. :cool:

Edited by herbal space program

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