Vector engine possibly a little too good?

[KerbMav]

I tend to agree.

On the other hand the Vector was meant to launch a shuttle, a shuttle as players know it in the real world - regularly a large craft, and also has to carry all the fuel to get it into orbit in one stage (ignoring the two traditional two solid boosters here). So the engine has to deliver the power to do this.

An alternative design choice - for an engine introduced for this specific reason - might have been an engine assembly similar to the Mammoth: three nozzles with the middle one gimbaling, formfitted to go with the typical shuttle parts. The Mammoth consists of 4 nozzles and delivers "1000kn per nozzle" (4000kn), but you cannot take it apart and use it as an "overpowered 1000kn" 1.25m engine, it has to go with 3.75m parts.

Saying that the Vector is not meant to be used as any other 1.25m engine is no good, as it still can be used as such - and why should it not, it is there. Yet it goes against the former (implied) design principle in KSP, that no part should go unused/get obsolete due to newer parts later in the tech tree.

[Red Iron Crown]

I see your point, but the Vector isn't supposed to be used in 1.25m stacks to begin with. You may argue that's not the case for any other engine, but the numbers don't say anything out of ordinary. It's just the square cube law in effect.

It's a 1.25m engine, it's hardly unpredictable that it would be used on 1.25m stacks whether it is "meant to" or not.

[Streetwind]

On the other hand the Vector was meant to launch a shuttle, a shuttle as players know it in the real world - regularly a large craft, and also has to carry all the fuel to get it into orbit in one stage (ignoring the two traditional two solid boosters here). So the engine has to deliver the power to do this.

A shuttle as players know it in the real world works quite differently, though. On the STS, each of the three RS-25 engines only contributed about 6% to the liftoff thrust. The remaining 82% came from the two solid motors. No, the liquid engines on the shuttle were never about delivering power. The RS-25 is a sustainer engine with moderate thrust and good vacuum performance; by the time they had to support the shuttle on their own, they were essentially acting as an upper stage engine.

But in KSP, our biggest solid motor has an anemic 670 kN thrust. If we took the Kickback as a baseline, the closest thing to matching engines for a STS replica would be a trio of Terriers. Meanwhile, each Vector alone puts out 1,000 kN, and the Isp is closer to that of a true sea level engine. Apart from the large gimbal range, it's really nothing like a RS-25 at all (and the Kickback is nothing like a shuttle booster at all either).

[KerbMav]

While I did not know everything you wrote, my statement is still valid, the Vector as to carry the shuttle to orbit (in KSP).

But I am on the same page with you that it is not confined to this sole purpose and therefore outshines the other 1.25m engines to much.

[More Boosters]

It's a 1.25m engine, it's hardly unpredictable that it would be used on 1.25m stacks whether it is "meant to" or not.

Well, the hidden meaning here is that 1.25m stacks at late game are usually for launching small probes and stuff. You don't use Mainsail on every 2.5m stack, so you don't use Vector on every 1.25m stack, but 1.25m stacks at late game generally don't carry anything heavy. I can think of 1.25m stacks where I wouldn't need to place 10 FL-800s to tame the Vector.

@Streetwind

Everything I find for the SSME suggest a higher thrust and lower weight though I am guessing the orbiter was larger than our Mk3 parts.

Edited November 10, 2015 by More Boosters

[Streetwind]

You don't use a Mainsail on every 2.5m stack, because you have other options that are just as good. But in the Vector's case, every other option is vastly inferior.

The Vector compares to a Swivel like a Mainsail compares to a Skipper that weighs twice as much as it normally does.

EDIT: Of course I'd still use a Swivel if it's enough to launch the payload, even if the Vector is so much better. That's a natural decision. But my point is, the Swivel runs into a limit far more quickly than the Skipper does, because the Swivel is really bad compared to the Skipper. If there was a 1.25m engine that is comparable to the Skipper - like, a Swivel with ~350 kN thrust - then the Vector would feel far more sensible. But there isn't.

Edited November 10, 2015 by Streetwind

[More Boosters]

You don't use a Mainsail on every 2.5m stack, because you have other options that are just as good. But in the Vector's case, every other option is vastly inferior.

The Vector compares to a Swivel like a Mainsail compares to a Skipper that weighs twice as much as it normally does.

Yes and you pointed out wonderfully, Reliant/Swivel are anemic. The Vector's also more expensive than a Mainsail with the same TWR, you pay for the compactness and the gimbal. I will however say that there's no reason to use anything but a cluster of Vectors outside career mode for lifting, but the differences are academic. And Vector has both less thrust and more weight than the SSME, it just so happens that our kickback is nothing like the 3.71m monstrosities the real life shuttle SRBs are. Thing's out of scale for sure, the Vector has its real size while the Kickback's diameter is a third of its real life counterpart. And I think it's supposed to be the 5-segment variant for SLS.

Counter-edit: I think you're making a wonderful case for buffing Swivel, it just so happens that you're using that against the Vector and not for the Swivel.

Edited November 10, 2015 by More Boosters

[Frozen_Heart]

The Vector has to be so OP simply due to the fact that we have no good SRBs. The real shuttle SRBs provided almost all of the thrust up to a pretty good altitude and speed. Try that with KSPs strongest SRBs... you won't even leave the pad. Even if you do they burn out incredibly quickly. In addition the shuttles SRBs gimballed and had reducing thrust to keep the stack balanced.

[r_rolo1]

Well, all of this discussion about the Vector vs the Swivel makes me remember other 1,25 m engine that is sorely underpowered ( compared with RL stats ): our dear friend T1, aka aerospike, that had it's thrust nerfed a long long time ago due to gameplay considerations that don't make sense nowadays. Everytime I see the thrust they have in game and remember the almost 1 MN at sea level of the real life XRS-2200 I shake my head in disbelief ...

Well, on the Vector itself, I agree with the posters that say that the Vector itself is not ( that ) overpowered, but the transition between the early 1,25m engines to the more high tech and recent ones is way too abrupt. It would make sense to have something in between.

EDIT: Oh, and the SRB we have in game are few and in general underpowered compared with the RL SRB. That also does not help

Edited November 10, 2015 by r_rolo1

[Frozen_Heart]

Just been doing some scrap paper calcs and I think that 600 - 650 could make a good ASL thrust for the vector. Though this would mean we would need a SRB with a thrust of 2500 - 3000 ASL.

3 of these and a pair of the SRBs provides about the correct amount of thrust for a shuttle and in the right ratios.

[More Boosters]

Just been doing some scrap paper calcs and I think that 600 - 650 could make a good ASL thrust for the vector. Though this would mean we would need a SRB with a thrust of 2500 - 3000 ASL.

3 of these and a pair of the SRBs provides about the correct amount of thrust for a shuttle and in the right ratios.

You do realize, that the Vector is both heavier and weaker than the SSME? (Also less efficient as the real SSME uses LH2)

The problem here is simple, SRBs are far too weak and Kerbin is small.

[paul23]

Well isn't the solution then to add a better tier of solid fuel boosters? A booster that has bad Isp, but has an empty weight vacuum thrust of about 1000 kN. Maybe a 2.5m width, size of the BACC booster? It would have a atmospheric thrust of 1300 kN, a vacuum thrust of 1400. 3240 "" fuel (no unit given for others, but two times the radius, means 4 times the amount of fuel). Empty mass would be 3 (2 times back - since the circle circumference only grows linearly with radius). An Isp of (185.42-199.68) seconds.

This would give the engine a full weight of 27.3 tonnes. And the TWR would be:

Sea level: (4.85 - 44.2)

Vacuum: (5.23 - 47.5)

Now the actual TWR isn't exceptional when it's full, but since it's so heavy it's more important to notice the free thrust, how much thrust has it left over to actually "lift" something. At full tanks:

Sea level: (4.67 - 1) * (27.3 * 9.81) = 1032 kN => ~105 tonnes extra mass

Vacuum: (5.23 - 1) * (27.3 * 9.81) = 1133 kN => ~115 tonnes extra mass.

The burn time would be: 34 seconds.

Compare the extra lifting power to the kickback: only 36.5 tonnes.

As for the vector: I'd really like to see a small reduction in thrust: to something of 750-800. With a similar reduction in mass (so the same engine TWR to keep it competitive lategame). That would at least open options for more high-thrust engines and solid fuel boosters. Without starting a massive power creep now already.

Edited November 10, 2015 by paul23

[Frozen_Heart]

You do realize, that the Vector is both heavier and weaker than the SSME? (Also less efficient as the real SSME uses LH2)

The problem here is simple, SRBs are far too weak and Kerbin is small.

That is the case with all KSP engines... I was using KSP values not real life ones.

[Streetwind]

As for the vector: I'd really like to see a small reduction in thrust: to something of 750-800. With a similar reduction in mass (so the same engine TWR to keep it competitive lategame). That would at least open options for more high-thrust engines and solid fuel boosters. Without starting a massive power creep now already.

Doesn't work. You'd have to reduce its weight to 3 tons. That suddenly makes it become a Skipper with 100 more thrust in a smaller form factor.

[cantab]

As I see it the problem comes back to the ARM pack being done all wrong. To follow the real SLS each Kickback should have around twice the thrust of a Mammoth. So if the total liftoff thrust of a KSP SLS had stayed the same, we should have had Kickbacks delivering 2000 kN each ASL, a Mammoth delivering 1000 kN, and a Vector delivering 250 kN. Then the Vector would look pretty normal, though chances are it would still beat the Skipper Swivel on vacuum Isp and TWR.

Even if the Mammoth had been something like 2000-3000 kN (because less thrust than the Mainsail might raise eyebrows), that would still have lead to a better Kickback and a more sensible Vector.

Edited November 10, 2015 by cantab

[More Boosters]

As I see it the problem comes back to the ARM pack being done all wrong. To follow the real SLS each Kickback should have around twice the thrust of a Mammoth. So if the total liftoff thrust of a KSP SLS had stayed the same, we should have had Kickbacks delivering 2000 kN each ASL, a Mammoth delivering 1000 kN, and a Vector delivering 250 kN. Then the Vector would look pretty normal, though chances are it would still beat the Skipper on vacuum Isp and TWR.

Even if the Mammoth had been something like 2000-3000 kN (because less thrust than the Mainsail might raise eyebrows), that would still have lead to a better Kickback and a more sensible Vector.

Are you saying Mammoth's 4000 kn is overpowered?

[Gaarst]

Are you saying Mammoth's 4000 kn is overpowered?

I'd say unbalanced.

That or the Mammoth is indeed overpowered and SRBs underpowered.

[More Boosters]

I'd say unbalanced.

That or the Mammoth is indeed overpowered and SRBs underpowered.

SRBs are underpowered for sure, they cut off far too early. But that doesn't make mammoth OP imo.

[r_rolo1]

Well, cantab was not defending cutting down the Mammoth AFAIK. He was just saying that the LFO engines of the 0.23.5 update were far stronger in comparison with the SRB of the same update and that even if the Mammoth was scaled back, that would still hold true.

[cantab]

Are you saying Mammoth's 4000 kn is overpowered?

Viewed as a game element, it's OK. Because it's the biggest and heaviest engine it's not a big problem if its TWR and Isp outclass smaller stuff because it can't replace that smaller stuff anyway. Viewed as an analogue for the real SLS engines, it's all wrong.

[More Boosters]

Viewed as a game element, it's OK. Because it's the biggest and heaviest engine it's not a big problem if its TWR and Isp outclass smaller stuff because it can't replace that smaller stuff anyway. Viewed as an analogue for the real SLS engines, it's all wrong.

Its TWR is 16/15 times Mainsail's. 4000 kN is fair, it's like 2/3rds of the real thing and its heavier too. The mammoth is fine, what's all wrong is the Kickback.

[paul23]

Doesn't work. You'd have to reduce its weight to 3 tons. That suddenly makes it become a Skipper with 100 more thrust in a smaller form factor.

Wait, that means this engine is already -even heavy weight- a far superior option than the skipper.

In what craft would you put the skipper instead of the vector (+ a few struts to prevent wobbling)?

[More Boosters]

Wait, that means this engine is already -even heavy weight- a far superior option than the skipper.

In what craft would you put the skipper instead of the vector (+ a few struts to prevent wobbling)?

Well, Skipper has a worse TWR and gimbal range but it is lighter and more efficient. Also like a third as expensive as Vector.

[Norpo]

Wait, that means this engine is already -even heavy weight- a far superior option than the skipper.

In what craft would you put the skipper instead of the vector (+ a few struts to prevent wobbling)?

The skipper has slightly (5) better vacuum isp, but that's all as far as I can tell, aside from the obscene cost the Vector has.

EDIT: You know what might balance the Vector? Remove it's bottom attachment point; that way it's strictly a first stage engine, either that or you bend your entire craft around to include it elsewhere.

Edited November 10, 2015 by Norpo

[paul23]

To show how they are often employed in real life, here you see a fokker-100 with it's thrust reversal on:

Thrust reversal is quiet effective, though the airworthiness regulations state that the specification (minimum landing distance etc) may not depend on active braking such as thrust reversal. (Consider a landing when the engine's have failed, it would be a shame to land succesfully and then notice you drop in the sea at Singapore due to no thrust reversals).