Has the atomic rocket lost some of its power?

[Silverwood]

I recently tried to use the atomic rocket to move a rocket from Kerbin (300K oribit) to Duna. I needed thrust of around 3000. The rocket burned for many minutes with 400  tank, got to around 2500 and ran out of fuel. I then retried replacing the atomic rocket with a normal rocket - the poodle if I recall, anyhow it achieved the burn with some fuel remaining.

So have the spces for the atomic rocket changed? 

Keith

[Rocket In My Pocket]

Nothing has changed, the Poodle has always had way more thrust than the Nerv.

That's what the Nerv does well, very low thrust but extremely efficient.

You were using only Liquid fuel with the Nerv right? It doesn't need Oxidizer. Also, how much mass are you trying to move here?

[Silverwood]

Hi

Yes I only had liquid fuel, the total mass of that section was 62.735, but the speed in orbit was low - under 1900, so it had a fair whack to make up. I have since added some extra tanks to the first stage, which now gets me into orbit with almost half fuel left. That alone gave me a total exit speed of 3400! Even before engaging the next stage. So looks like I don't need the nerv after all. Having said all that I have yet to complete the actual two way trip!

I would be interested to hear how other people have made it to Duna and back early in the game.

Keith

[bewing]

You'd probably do a lot better with the nuke by lowering your Pe to be right around 70km at the point you are doing your ejection burn.

[Greenfire32]

I'm about to commit a kerbal sin here, but I've never used the nerva engines because their thrust is just too low. In order to get any kind of decent push from them you need at least 2 (4+ preffered) and by then it gets hard to stick it onto an ascent vehicle and it's heavy and the weight vs economy cost is weird.

I know, I know, efficiency and inter-planetary burns, I KNOW.

I cant do it. I just cant sit in the same orbit burning at PE over and over and over and over until I FINALLY manage to reach escape velocity. Screw it. I'll just take 3,000,000,000 more tons fuel and use a "proper" rocket. At least that way I don't have to play 78938746D chess with maneuver nodes. 1 burn, 1 node with good 'ol liquid fuel engines.

I said I KNOW, alright!

[Silverwood]

Well if we are admitting 'sins' here....I did not realise the Pe was the best place for the burn!

[Zeiss Ikon]

I've never used a NERV, either.  Too expensive, too heavy for the thrust, and not enough better than a Poodle (or, now, Wolfhound) to justify for anything closer than Dres.  Maybe, if you're going to Jool, Eloo, or Moho, and need to take Kerbals or something else heavy (hence ruling out ion engines due to even lower thrust), the NERV would make sense.  I haven't flown such missions yet (career hasn't gone past Minmus yet, and my old Science game had only achieved Duna flyby and Gilly landing).  In fact, for my Duna flyby, I used a Rhino for the transfer stage.

[blakemw]

19 hours ago, Silverwood said:

I would be interested to hear how other people have made it to Duna and back early in the game.

 

Depending on how early you mean.... I actually usually do get LV-N before going to Duna. Often you can pick it up with a test contract, so if "early" is 160 science nodes and some 300, then my favored stack looks exactly like this: https://kerbalx.com/blakemw/LV-N-Lander-with-Launcher (Twin-Boar w/ solids, Skipper, LV-N). The Twin-Boar gets the thing mostly into orbit, the Skipper handles the remaining and does the ejection burn maybe some capture burn too. The LV-N lander is for hopping all over Ike and finally hitting a couple of biomes on Duna before going home.

With even lower tech, well I don't see why you would, there is plenty of science from Mun/Minmus to unlock the good 160/300 parts and Gilly is also an easy target. But basically Skipper w/4xThumper -> Poodle -> Terrier. Something like that should be enough to put 2 Kerbals on Ike and Duna and bring them home. I wouldn't want to do it without the 2.5m parts though of course anything is possible.

Duna requires less dV to land on than the Mun does. Coming home then requires about 2000m/s from the surface of Duna, more or less depending on streamlining and TWR.

Edited April 10, 2018 by blakemw

[Superfluous J]

I only use the Nerv for getting to Moho. All other targets don't need that much efficiency and I'd rather have shorter burn times.

I also sometimes use them for a big Jool ship, but that's pretty rare.

But I always use more than one, and always drop them once the mass or dv needs drop low enough.

To answer the specific "how do you get to Duna?" question: Terriers.

Edited April 10, 2018 by 5thHorseman

[Silverwood]

5 hours ago, blakemw said:

Depending on how early you mean.... I actually usually do get LV-N before going to Duna. Often you can pick it up with a test contract, so if "early" is 160 science nodes and some 300, then my favored stack looks exactly like this: https://kerbalx.com/blakemw/LV-N-Lander-with-Launcher (Twin-Boar w/ solids, Skipper, LV-N). The Twin-Boar gets the thing mostly into orbit, the Skipper handles the remaining and does the ejection burn maybe some capture burn too. The LV-N lander is for hopping all over Ike and finally hitting a couple of biomes on Duna before going home.

With even lower tech, well I don't see why you would, there is plenty of science from Mun/Minmus to unlock the good 160/300 parts and Gilly is also an easy target. But basically Skipper w/4xThumper -> Poodle -> Terrier. Something like that should be enough to put 2 Kerbals on Ike and Duna and bring them home. I wouldn't want to do it without the 2.5m parts though of course anything is possible.

Duna requires less dV to land on than the Mun does. Coming home then requires about 2000m/s from the surface of Duna, more or less depending on streamlining and TWR.

Ok - I clearly need to rethink this. I have probably half the tech tree unlocked - but have tended to stay with fairly simple designs. Usually a capsule & shield for re-entry, a fuel tank and poodle for the return. Then the first stages were mainsail engines - 4 - with three fuel tanks, and another poodle with a fuel tank for the outward flight. Your ideas seem better.

[Greenfire32]

23 hours ago, Silverwood said:

Well if we are admitting 'sins' here....I did not realise the Pe was the best place for the burn!

If your orbit is circularized really well, it doesn't matter a whole lot (but a little bit) where you burn since you'll mostly be at the same altitude and speed the entire time, but if your orbit is only roughly circular or completely oblong, then you'll want to burn at Pe. The reason for this is that you'll be traveling the fastest at your lowest point in the orbit (the closer you are to a body, the faster you move). So if you burn at that point, you'll affect your Ap with far greater efficiency.

^ That is a super hilariously condensed lesson on what is known as the "Oberth" effect that you can read more about here: https://en.wikipedia.org/wiki/Oberth_effect

This is really only used for transfer burns between two bodies and since Nerva engines are usually used for inter-planetary burns, the result is that you'll end up sitting in a slowly increasing orbit for days and weeks because Nerva's thrust is so low that you often times won't reach escape velocity on 1, 2, 3, or maybe even 4 burns at Pe unless you bring a ton of them which...eh I'll just use LF engines at that point.

[GoSlash27]

On 4/9/2018 at 10:39 AM, bewing said:

You'd probably do a lot better with the nuke by lowering your Pe to be right around 70km at the point you are doing your ejection burn.

bewing,

Surprisingly, this is not the case. The gate altitude to Duna is almost 8 Mm, so it's cheaper for him to burn direct from 300k than it is to lower his Pe.

On 4/9/2018 at 10:09 AM, Silverwood said:

I would be interested to hear how other people have made it to Duna and back early in the game.

I do it from low Munar orbit using a Poodle.

Best,
-Slashy

[Norcalplanner]

2 hours ago, GoSlash27 said:

Surprisingly, this is not the case. The gate altitude to Duna is almost 8 Mm, so it's cheaper for him to burn direct from 300k than it is to lower his Pe.

I harbor illogical warm feelings towards that thread where we all learned about gate orbits. Good times... [sniff] 

[Aegolius13]

On 4/9/2018 at 10:02 AM, Greenfire32 said:

and by then it gets hard to stick it onto an ascent vehicle and it's heavy and the weight vs economy cost is weird.

If you have Making History,  the engine plates make it much easier to work with clustered engines like this.   But then of course there's still the lack of good LF-only tanks...

[DerekL1963]

24 minutes ago, Aegolius13 said:

But then of course there's still the lack of good LF-only tanks...

That's the biggest problem with using NERV's...  if you're going to make effective use of them, you have to have a fuel tank editing mod.

[bewing]

It all depends on your ship design preferences. You have MK1, MK2, and MK3 LF tanks. If your ships are small, then your burn times are reasonable.

But nukes make the most sense when you are refueling your craft. Maybe they don't make so much sense the first time you fly them someplace. Once you fly back to Minmus, refill them with another load of lf, and fly off again ... by that point the mass savings starts to become extreme.

 

[TheFlyingKerman]

On 2018/4/9 at 11:09 PM, Silverwood said:

I would be interested to hear how other people have made it to Duna and back early in the game.

I just use the basic 1.25m engines - 2 Thumpers and 2 Reliants for booster, 1 Swivel for core stage, 1 Terrier for transfer, 1 Terrier for ascend and going home.

[Silverwood]

1 hour ago, TheFlyingKerman said:

I just use the basic 1.25m engines - 2 Thumpers and 2 Reliants for booster, 1 Swivel for core stage, 1 Terrier for transfer, 1 Terrier for ascend and going home.

Aha, that sounds like a good simple idea.

I assume just a single Kerbal as well? I will try that version. My most recent attempt, gets me there...but the lander is too heavy. I relied on parachutes, which was a mistake!

 

[radonek]

On 9. 4. 2018 at 5:09 PM, Silverwood said:

I would be interested to hear how other people have made it to Duna and back early in the game.

Top up last booster stage and use that for transfer burn. This usually means Skipper or Poodle. If I were to use Nerv, I'd pull AP to some decent height, cirularize, top up again and do transfer  burn from there. It may not be most efficient, but navigating tanker ships around Kerbin system is trival, while dealing with long burns in LKO is not.

[TheFlyingKerman]

On 2018/4/11 at 3:58 PM, Silverwood said:

Aha, that sounds like a good simple idea.

I assume just a single Kerbal as well? I will try that version. My most recent attempt, gets me there...but the lander is too heavy. I relied on parachutes, which was a mistake!

 

Yes, single Kerbal. Note that I use 4 MK16 and a drogue parachute for landing on Duna, and with a light ship it is not so different from landing on Kerbin.

[Silverwood]

Ok thanks.

I can't quite see what the bottom stage is? And I do not see what to tapered section is either?

 

 

[LameLefty]

To answer the original question, it seems to me I remember the NERV being nerfed at some point, maybe the run-up to the 1.0 release. I think ISP used to be substantially higher. Even with the same thrust, the much higher ISP made its use for interplanetary transfer stages much more mass-effective. 

Edited April 13, 2018 by LameLefty

[GoSlash27]

10 hours ago, LameLefty said:

To answer the original question, it seems to me I remember the NERV being nerfed at some point, maybe the run-up to the 1.0 release. I think ISP used to be substantially higher. Even with the same thrust, the much higher ISP made its use for interplanetary transfer stages much more mass-effective. 

I don't recall any reduction of the LV-N's Isp although the mass went up from 2.25t to 3t in KSP 1.0. It also had some major overheating issues that were cleared up quickly.

I rarely use the LV-N myself in career, mainly due to the cost.

Best,
-Slashy