1.25m Mid-Level First Stage Engine

[Silavite]

Inspired by this post: 

 

One of the things that irks me about the 1.25m parts is that lack of an engine reasonable in capability but not excessively expensive for launches. The Reliant is an early game engine and it shows, with a TWR of 16.7 at sea level and 19.6 in a vacuum. The high-end 1.25m, the Vector, produces a very impressive TWR of 23.9 at sea level and 25.5 in a vacuum. For the purposes of comparison, the venerable Mainsail manages a TWR of 23.45 at sea level and 25.5 in a vacuum.

The following is what I would propose for the characteristics of an engine that fills the gap outlined above. Others may differ, but my opinion for the stats of such an engine are roughly as follows:

• 1.8 tons
• 360 kN in Vacuum (TWR 20.41)
• 325.16 kN at Sea Level (TWR 18.43)
• 310 ISP in Vaccum
• 280 ISP at Sea Level
• 2° of vectoring
• 2,650 funds cost

The stats of this hypothetical engine also reflect consideration of its other competitor: the Aerospike. It is superior to the Aerospike for low altitude flight (better TWR, gimbaling, cheaper) but remains inferior at higher altitude (heavier, worse vacuum ISP).

What do you guys think about it? Do you think such an engine gap exists, and if so, would you agree at least roughly with my hypothetical stats?

[NotAgain]

45 minutes ago, Silavite said:

Do you think such an engine gap exists, and if so, would you agree at least roughly with my hypothetical stats?

I honestly hadn't particularly noticed the engine gap, but, now I look, it makes loads of sense. I like the stats, they seem reasonable, but perhaps vaccum isp shold be a wee bit lower, 305, maybe?

[Benji13]

That sounds like a good idea. Basically a 1.25m engine that's better than the early ones but only decent for launches. Someone should make a mod for this. If anyone wants to do this and needs help, I'm good with cfg's and ok at modelling. 

[Stef Morojna]

10 hours ago, Silavite said:

Inspired by this post: 

 

One of the things that irks me about the 1.25m parts is that lack of an engine reasonable in capability but not excessively expensive for launches. The Reliant is an early game engine and it shows, with a TWR of 16.7 at sea level and 19.6 in a vacuum. The high-end 1.25m, the Vector, produces a very impressive TWR of 23.9 at sea level and 25.5 in a vacuum. For the purposes of comparison, the venerable Mainsail manages a TWR of 23.45 at sea level and 25.5 in a vacuum.

The following is what I would propose for the characteristics of an engine that fills the gap outlined above. Others may differ, but my opinion for the stats of such an engine are roughly as follows:

• 1.8 tons
• 360 kN in Vacuum (TWR 20.41)
• 325.16 kN at Sea Level (TWR 18.43)
• 310 ISP in Vaccum
• 280 ISP at Sea Level
• 2° of vectoring
• 2,650 funds cost

The stats of this hypothetical engine also reflect consideration of its other competitor: the Aerospike. It is superior to the Aerospike for low altitude flight (better TWR, gimbaling, cheaper) but remains inferior at higher altitude (heavier, worse vacuum ISP).

What do you guys think about it? Do you think such an engine gap exists, and if so, would you agree at least roughly with my hypothetical stats?

It does sound reasonable from the point of view of a experienced player,  but for a new player this would only create confusion.

Heck for me even having the 30 and 45 gimbal versions was a lot of confusion when I started.

[Silavite]

On 12/3/2016 at 0:35 PM, Stef Morojna said:

It does sound reasonable from the point of view of a experienced player,  but for a new player this would only create confusion.

Heck for me even having the 30 and 45 gimbal versions was a lot of confusion when I started.

Hmm... fair enough. My first space game was Orbiter 2010, and I had been watching Scott Manley's videos for a few months before I got KSP, so I was fairly adept at spaceflight and its various terms even as a new player. Perhaps putting it in Advanced Rocketry (the same tech node that unlocks the Terrier) to contrast it with the Terrier would help? The description could even be something along the line of;

Quote

After Kerbal engineers repeatedly managed to blow up every attempt at making a suitable low altitude engine, an engineer working on the RE-I5 "Skipper" mistakenly ordered all the parts for it in half-size. Amazingly, this accident produced a fine first stage engine that did not blow up. It was quickly christened the RE-I2.5 "Sailor" and boasts an illustrious service record (at least, none of the accidents were caused by the engine blowing up) as a low altitude engine, especially when used in conjunction with the LV-909 "Terrier" upper stage engine.

I think the description, combined with it being unlocked with the Terrier, should help players understand its function.

Edited December 5, 2016 by Silavite
clarification

[GluttonyReaper]

I know it's not happening any time soon, but I liked the way the Porkjet revamp handled it - keep the Reliant as an early-game engine, but have it upgrade to a decent lifting engine through the tech tree, while leaving the Swivel as a nice mid-range.

 

(and then formally make the Vector a 2.5m engine, so people stop trying to compare it to the 1.25m engines all the time )

[OrbitalBuzzsaw]

What about a stock SpaceY Kiwi (and stock SpaceY in general, for that matter)?

Edited December 5, 2016 by OrbitalBuzzsaw

[Streetwind]

This kind of thing doesn't even need that much development effort.

KSP has natively supported PartUpgrades since 1.2.0. This lets you put a dummy item into a later tech node in the tech tree which, upon unlocking, changes the stats of one or more previously unlocked parts. This would allow you to, for example, both have the LV-T30 as an earlygame engine, and also transform it into a variant with higher thrust as the player progresses through the midgame. No mods required.

Porkjet's example parts download comes with several such PartUpgrades implemented, if you want to check it out. There's an outstanding issue right now where the editor doesn't support displaying the upgraded stats (you need to add the part to your ship first and then rightclick it), but otherwise it's fully functional. And will probably be expanded upon in the future.

Edited December 8, 2016 by Streetwind

[Sharpy]

One question: what practical application would that engine serve? What would it do, that you can't achieve with Kickback and Terrier?

By the time Reliant ceases to be a viable option, you have the 2.5m parts for heavier payloads and really don't care about atmospheric LF/OX engines much. Aerospike and Rapier fill the gap nicely for spaceplanes, Aerospike being generally a very neat option everywhere where Vector would be an overkill. You want to launch heavier payloads on 2.5m boosters anyway, and for light payloads, Kickback combined with Terrier or LV-N are superior.

While I see that "gap" in the 1.625m "market", I don't think it really matters, because I can't see any practical applications that would fall into that gap.

[Silavite]

12 hours ago, Sharpy said:

One question: what practical application would that engine serve? What would it do, that you can't achieve with Kickback and Terrier?

By the time Reliant ceases to be a viable option, you have the 2.5m parts for heavier payloads and really don't care about atmospheric LF/OX engines much. Aerospike and Rapier fill the gap nicely for spaceplanes, Aerospike being generally a very neat option everywhere where Vector would be an overkill. You want to launch heavier payloads on 2.5m boosters anyway, and for light payloads, Kickback combined with Terrier or LV-N are superior.

While I see that "gap" in the 1.625m "market", I don't think it really matters, because I can't see any practical applications that would fall into that gap.

Egads! You make an excellent point about the Kickback. I very rarely use SRBs as core stages so the concept never crossed my mind when writing this. I suppose that the hypothetical engine could be an alternative for the Kickback as a core stage in 1.25m rockets, and as liquid fueled boosters when a little bit more ΔV is desired without adding an extra stage. That, and the fact that being throttleable adds an extra degree of flexibility.

Edited December 14, 2016 by Silavite

[Aegolius13]

On 12/3/2016 at 10:35 AM, Stef Morojna said:

• 1.8 tons
• 360 kN in Vacuum (TWR 20.41)
• 325.16 kN at Sea Level (TWR 18.43)
• 310 ISP in Vaccum
• 280 ISP at Sea Level
• 2° of vectoring
• 2,650 funds cost

That's approximately what you get with three Thuds, other than the mass.  Like many folks on here, I find the Thud pretty clunky and don't like to use it. But there's definitely a lack of good small-to medium launch engines right now.  The Swivel is no longer efficient or powerful as a launch engine; the Reliant is OK in terms of power but the lack of gimbal is problematic; the Dart is not that well-suited due to no gimbal and high cost.  So, by necessity, I've started adding Thuds to rockets too big for a Swivel but too small for a Skipper.

Rather than using three Thuds (threes are not great for stability), to get close to the performance you describe I'd probably go with a Reliant and two Thuds. That uses the bottom node, gets you better TWR and not much change to ISP.  

One other option is to use a disposable jet (e.g., Whiplash) based booster rig.  They start slow, but generate a whole lot of power once they get going.  And the cost savings from all the fuel you don't need can help offset the higher engine cost.

Finally, @Snark came up with a mod to convert the Vector into an engine kinda like what you mention, but higher efficiency I think.  However, it might get confusing if you want to keep that, plus the regular Vector, since they'll look the same.  

 

 

[septemberWaves]

I think we definitely need an engine for this gap. I'd prefer about 400KN thrust though, because then you could stick two or three of them on the bottom of a 2.5m rocket and have a good mid-range engine cluster between the Skipper and the Mainsail.