Nervs of steel

[Palaceviking]

Pls help, I desperately need to prove a point  go to tylo on nervas and land with them,  obviously using the lander as the tug for the fuel etc, before I get all high and mighty about how great the nerva is,  is this even possible?  Am I going to end up looking like a fool? 

Especially for you..

@Spricigo

[steuben]

Going to Tylo on Nervs is trivial and left as an exercise for the class.

Given that Tylo has no atmosphere nervs will work. A mk1-2, 4 Nervs, and 5 mk1 fuel tanks give 4k/s dv which according to the subway map should be enough to land without lithobraking.

[Geschosskopf]

47 minutes ago, Palaceviking said:

Pls help, I desperately need to prove a point  go to tylo on nervas and land with them,  obviously using the lander as the tug for the fuel etc, before I get all high and mighty about how great the nerva is,  is this even possible?  Am I going to end up looking like a fool? 

While it's true what @steuben says, you CAN land on Tylo with nukes, it's not just as simple as just having the requisite dV,  You also need to plan your descent profile in accordance with your TWR.  The real trick to landing on Tylo isn't getting to the ground before the fuel runs out, it's getting to the ground slow enough to survive the landing.  TWR determines how long it will take you to lose all your orbital velocity, so your descent profile needs to give you that much time between initial de-orbit and reaching the surface.  Of course, you need enough fuel to run the engines that long, too, but that's really not the hard part, because the more fuel you have, the less TWR you have.

Therefore, every given Tylo lander has an optimum descent profile.  The techniques you use everywhere else usually won't work on Tylo---you'll have to do some figuring and trial-and-error testing.  Descent profile means both the altitude you starts at and the angle you come down at.  The lower you start, the more shallowly you have to come down and vice versa, so you can spend the required amount of time between starting and the ground.  Nukes aren't known for TWR, so you need to give yourself lots of room.  I recommend designing the lander in a test game, then HyperEditing it to Tylo and experiment until you can land safely.  Write down what you did, then fly the real mission and land that way when you get to Tylo.

[Palaceviking]

Cheers,  I'm doing it in career(got a spare million bucks) and I'm thinking constant altitude landing?  Though I've never used the technique before!

[Foxster]

See, the basic thing about your "constant altitude" approach to a landing is that, ultimately, it means you never reach the ground. 

You are a bit better with a "constant slightly falling altitude" landing really.

To be a tad more serious though...Tylo and back to orbit on nukes is quite do-able but not trivial. Just keep the payload to the absolute minimum and you'll be good.   

[Human Person]

Well, count me in as one of the guys opposing you in proving your point. Using Nervs for a Tylo lander is redicolous, because Nervs aren't good for high TWR craft, they'r entirely too heavy for that.

Edited September 20, 2017 by Physics Student

[Palaceviking]

29 minutes ago, Physics Student said:

Well, count me in as one of the guys opposing you in proving your point. Using Nervs for a Tylo lander is redicolous, because Nervs aren't good for high TWR craft, they'r entirely too heavy for that.

As long as I don't carry a redicolous amount of fuel to the surface I should be OK though?

[Geschosskopf]

46 minutes ago, Physics Student said:

Well, count me in as one of the guys opposing you in proving your point. Using Nervs for a Tylo lander is redicolous, because Nervs aren't good for high TWR craft, they'r entirely too heavy for that.

It's been done, many times by many people over a span of many years.  Of course, the stats of the nuke engines have changed a lot over that time, but in general they've kinda evened out.  The thrust has stayed about constant but the Isp has gone down, which sounds bad.  But OTOH LVNs now burn only LF, not LFO, so you get more dV per unit of tank volume.

Personally, I find the best descent profile for a nuke Tylo lander is to start fairly high, usually 250-300km altitude, and come down about 90-120^ longitude around from where you start.  The higher you start, the lower your initial orbital velocity, putting it more into the range of what the LVN's low TWR can eliminate while fighting Tylo's desire to speed your descent.  Plus, the higher you start, the more accurately you can land at a specific target.

The low-altitude, almost-no-descent approach is really only suited to landers with huge TWR that aren't worried about landing in a specific place.  The lower you start, the higher your initial velocity, so the more work the engines have to do.  This translates into the lander covering a huge horizontal distance and landing wherever it is when in finally slows down to a reasonable landing speed.

 

Edited September 20, 2017 by Geschosskopf

[Human Person]

21 minutes ago, Geschosskopf said:

It's been done

I didn't say it isn't possible, I said it's redicolous.

 

@Palaceviking yes, it's possible, but your lander will be much heavier than one that uses chemical engines.

29 minutes ago, Palaceviking said:

As long as I don't carry a redicolous amount of fuel to the surface I should be OK though?

Edited September 20, 2017 by Physics Student

[Geschosskopf]

49 minutes ago, Physics Student said:

I didn't say it isn't possible, I said it's redicolous.

@Palaceviking yes, it's possible, but your lander will be much heavier than one that uses chemical engines.

Not necessarily.  As with any lander, the design of one for Tylo depends entirely on its mission.

• Payload:  Is this a probe or crewed?  If crewed, how many and are you using just external seats or do you require a pod?  Do you need life support?  Are you delivering something to Tylo, such as a rover, a base module, or a tank of resources?
• How many times does the lander need to land and/or take off?  Is this just about landing 1 time?  Is it about landing 1 time and returning 1 time?  Or do you need a reusable (as in 1-stage) shuttle that will have to make 2 or more round trips?
• Can you refuel on the surface or not?

Depending on where you fall in this range of possible lander designs, nukes may or may not be the best option.  Usually they're not, granted, but they do work pretty well for 1-piece shuttles whose only job is to move 1 Kerbal (MAYBE 2) in a pod (due to the radiation and assuming you need life support) between the surface and orbit, without refueling on the surface, but refueling in orbit.  Why would you do this?   It can happen.  Suppose you want a Kerbal to rover to all Tylo biomes.  So you land the rover as a 1-time landing-only thing uncrewed.  Then you send down the Kerbal in the reusable lander, which you have to land reasonably close to the rover (so need accuracy and high starting orbit).  While the Kerbal is driving all over Tylo, the lander goes back up and refuels in orbit.  There it waits in case the Kerbal wrecks the rover before reaching all the biomes.  Once the Kerbal has driven to all the biiomes, he parks the rover in an easily accessible spot for the lander, which goes back down and picks him up, then returns him to orbit.

Edited September 20, 2017 by Geschosskopf

[Draalo]

2 hours ago, Physics Student said:

I didn't say it isn't possible, I said it's redicolous.

From the point "build a Lander" it may be.

But i can easily imagine a mission where the NERVs bringing some benefit.

Using a lander attached to a bigger ship (MK3 crewcabin + MK3 Lf tank) make them usefull for the whole mission. In fact, you spare the weight of additional engines, also tanks for Ox if you want to fefill/reuse the lander.

[AeroGav]

Fun challenge,  I decided to try a compromise approach,  three NERVs and a Poodle.   Lock Retrograde on SAS,   control ROD by juggling thrust limiter on the poodle.

Started Retro burn on nukes only, at 40km bring the Poodle to 100% and on the last few hundred metres start throttling it again to control touchdown.

Made quite a few Kerbal omlettes this morning, as you can imagine.

We got back to orbit too, but the Poodle ran out of fuel about 12 seconds after liftoff.

Poodle has 1180dV and 0.77 TWR on its own, supplying 250kn.  The three NERVs supply another 240kn.

The lightest lander is probably a pure chem one with ISRU, but if you're not mining then the delta V requirement is so large a NERV almost makes sense.       I'm not very good with this kind of thing, since i'm unused to rockets, but the lander is economical in so far as only the Poodle and a relatively small tank is left behind.  On the other hand you could probably go lighter with a pure chemical rocket with more aggressive staging,   and though very little of the lander would be recoverable, you could get away with smaller boosters on kerbin as a  result.

[Spricigo]

21 hours ago, Palaceviking said:

Pls help, I desperately need to prove a point  go to tylo on nervas and land with them,  obviously using the lander as the tug for the fuel etc, before I get all high and mighty about how great the nerva is,  is this even possible?  Am I going to end up looking like a fool? 

Especially for you..

@Spricigo

I fail to notice whay that point is. I'm well aware that you can do a lot of things with nervs. If that is a good idea is an entirely other discussion. 

15 hours ago, Draalo said:

From the point "build a Lander" it may be.

But i can easily imagine a mission where the NERVs bringing some benefit

That seems like an adjustment to make the mission fit the equipment  rather than looking for what's tue best equipment for a given mission.  And I can easily imagine using nuclear propulsion to tranport the chemical lander being superior than both the pure chemical and the pure nuclear setup. 

1 hour ago, AeroGav said:

Fun challenge, 

I think that would be the ideal. Turning it in a full fledged challange with defined rules and score system. Than take the 'winners' as a demonstration of what a pure nuclear lander  can do and compare with chemical counterparts. 

Assuming the idea is to get that comparison. 

[Helmetman]

One could also be lithothrusting. Limit youself on TWR somewhat and put on detachable gear and use it similarly to lithobrake when you land. It probably depends per design how good this will work but I would look for a good spot with a slope on Tylo to do this.
I haven't done this myself though but it was just a thought at the top of my head. 

I'm sure one can lithobrake from 100-150m/s speed with some quikloading and the same for lithothrusting at similar speeds. Actually it's not really lithothrusting because you would still use the engines for thrust. I'm also not sure if lithothrusting is a proper term, but you probably know what I ment. (correct me if I'm wrong)

[AeroGav]

12 minutes ago, Helmetman said:

One could also be lithothrusting. Limit youself on TWR somewhat and put on detachable gear and use it similarly to lithobrake when you land. It probably depends per design how good this will work but I would look for a good spot with a slope on Tylo to do this.
I haven't done this myself though but it was just a thought at the top of my head. 

I'm sure one can lithobrake from 100-150m/s speed with some quikloading and the same for lithothrusting at similar speeds. Actually it's not really lithothrusting because you would still use the engines for thrust. I'm also not sure if lithothrusting is a proper term, but you probably know what I ment. (correct me if I'm wrong)

I think the term is lithobraking,  I did quite a lot of that, unfortunately couldn't use the vehicle (or the Kerbals) again afterward.

For a better example,  this infamous video

Spoiler

 

Spoiler - It later emerged he'd been editing the craft file (reducing its mass -  cheating !) to make this possible,   doesn't take away from what a well made and entertaining video this is.

It would be fun to resurrect this.    I think i could make it get to orbit with more fuel by building a space plane around the tank - then ditching those components above the atmosphere.   But I've no idea how to pull off gravity assists like that.

 

I do lithobrake on Minmus (this craft has one Vernor thruster as a low grav "vtol" thruster)  but Tylo ...  you'd be a brave Kerbal

 

Edited September 21, 2017 by AeroGav

[Helmetman]

@AeroGav I ment both lithothrusting and lithobraking.

But lithothrusting is the wrong term I guess. What I mean by that is you use less twr (just around 1) and use landing gear to accelerate on the surface and start gaining altitude by thrusting of a slope in order to get good positive climb rate and then coast all the way to orbit.

Now let's see the vids.

EDIT: Yeah, it shows it perfectly on the videos. I had actually quite lower speeds in mind for lithobraking so if your very good at it you should be able to go quite small or compact on tylo I think.

Edited September 21, 2017 by Helmetman

[Palaceviking]

I also have optional atmospheres installed but haven't found the options yet! Hope it won't hit the thrust too bad. 

 

Inspiring stuff though 

[Snark]

On 9/20/2017 at 9:59 AM, steuben said:

Given that Tylo has no atmosphere nervs will work. A mk1-2, 4 Nervs, and 5 mk1 fuel tanks give 4k/s dv which according to the subway map should be enough to land without lithobraking.

The issue isn't dV.  It's TWR, as several people have pointed out.  LV-N's aren't impossible to land with... but it's very challenging, because they only barely have enough TWR to be able to land there at all.

Tylo has a surface gravity of 7.85 m/s².  That means it's physically impossible to land unless you have more than 7.85 kN of engine thrust per ton of ship.  An LV-N has a thrust of only 60 kN.  That means that if you have an LV-N-powered lander coming down on Tylo, the absolute highest mass it can have is 7.64 tons per LV-N.  Since the LV-N itself is 3 tons, that leaves 4.64 tons per LV-N for the rest of the ship.  And note that realistically, your "mass budget" will be lower than that, since that's the absolute limit at which you can't actually decelerate when descending, but can only descend at constant speed.

For example, consider the lander that @steuben proposes above.  A Mk1-2 pod, four LV-Ns, and five Mk1 tanks would have a total mass of over 27 tons, even without taking into account other paraphernalia such as landing legs etc.  Let's be super optimistic and assume that you can bring the entire thing in at only 28 tons even.  It would have an acceleration of 8.57 m/s².  Since Tylo is 7.85 m/s² at the surface, that only leaves you only 0.72 m/s² of "excess" TWR that you can use to actually decelerate as you approach the surface.  With such wretchedly tiny deceleration, it means you'll have to spend a loooooooong time decelerating in the latter part of your burn, meaning you will pile up a lot of gravity losses (and likely cosine losses as well-- I expect a straightforward -all-the-way landing will be impractical, with such a low TWR).  Yes, by the time you get down to the vertical-descent part of your landing, you will have burned away a fair amount of fuel and thereby given yourself a little more TWR to play with, but it's still a tough challenge.

Does this mean it's impossible?  No.  You can land on Tylo with nukes, people do it.

But it does mean that the ship would be really really inefficient at landing:  the savings you get from the LV-N's high Isp tend to be more than thrown away by the inefficiencies of gravity and cosine losses.  So yes, you can do it... but it's hard, and takes a lot of attention to design, and the margin is very thin.

A side note, however:  I could totally see someone going with a "hybrid" approach, and spending a little bit of mass for a high-TWR "bump" at the end.  For example, the Spark is lightweight and fairly high TWR.  Three Sparks would mass only 0.3 tons, but have as much thrust as an LV-N.  So you could put a few Sparks (or similar) on there, with a small LFO tank to supply them just enough dV to cushion that last, mostly-vertical part of the descent.  (And ascent, if you plan on going back to orbit again.)  @AeroGav has kindly provided an example of this, above, though his design has a bigger investment in LFO (with a Poodle and a full 8 tons of fuel).

[Foxster]

Here's an over-engineered (stock) Tylo nuke lander as I don't think anyone posted one yet...

Edited September 25, 2017 by Foxster