What makes the 48-7S so good?

[SlabGizor117]

I've taken a look and although it has good thrust, the ISP isn't far from 1.25m engines. Maybe the TWR? Idk, just wondered.

Thanks!

-Slab

Edited February 22, 2015 by SlabGizor117

[Vectura]

The TWR is just through the roof, I almost never use the 909 because the 48-7S just ends up doing it better.

[RocketPilot573]

The TwR, High ISP, High thrust, and low weight is above normal compared to every other engine. Literally the ONLY time it's not the best choice is a heavy craft in vacuum (where nukes are best).

[SlabGizor117]

Huh, I'll keep that in mind. Thanks!

[GoSlash27]

High t/w, good Isp, and dirt- cheap. It's way out of balance with the other engines.

Best,

-Slashy

[zarakon]

Mostly the extremely high thrust/weight ratio

Other stats on it aren't great, but they're good enough

[cantab]

The TWR is excellent. That means a rocket stage needs less mass of engines, and that means more delta-V.

The Isp is good enough. It's not so bad as to undo the benefits of the high TWR.

It's small. That means it can be used on all sorts of craft, unlike say the KR-2L that's only any good on really big stuff.

In career mode it's the cheapest engine available, and you also unlock it early.

[Streetwind]

The high TWR is significant because it actually translates into dV.

All other engines have less TWR, and thus add more dry mass to the vessel. That means that in many situations, even engines with a higher Isp actually give you less dV than the 48-7S, especially if you carry only small amounts of fuel. Even the LV-909, which has 40 Isp more in vacuum, doesn't reach dV parity until the tanks get larger than most typical LV-909 missions require.

[Wabbit]

This thing puts the LV-1 out of business. It literraly beats the LV-1 in almost EVERY way. TWR, ISp, same weight. It's awesome. My typical 1.25m second stage is a cluter of these.

[Jouni]

The 48-7S is better than the other small engines, but it's no longer as overpowered as it was in 0.22 and 0.23. The LFB has a higher TWR than the 48-7S, the KR-2L has a higher TWR and a higher vacuum Isp, and the KS-25x4 has a higher TWR and a higher Isp. The Skipper and the Mainsail also beat the 48-7S in many circumstances, as long as the thrust requirements are close to an integer multiple of the thrust of a Skipper/Mainsail.

[SpacedCowboy]

Hi, I'm SpacedCowboy, and I'm a 48-7S aholic,,, Seriously though, what's going to happen to it when 1.0 drops? Really hope they don't mess with it too much.

[Starwhip]

Hi, I'm SpacedCowboy, and I'm a 48-7S aholic,,, Seriously though, what's going to happen to it when 1.0 drops? Really hope they don't mess with it too much.

Well, I wouldn't get my hopes up about that... "Rebalancing everything" generally includes everything, if you know what I mean.

[John FX]

Here is a set of charts showing which is the best choice for a single engine in vacuum for various payloads and TWR

Javascript is disabled. View full album

and here is one where the number of engines is unlimited

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As you can see the 48-7s is king for some parts, the nuke is king for others and the ION king for a lot of the rest, depending on the desired TWR.

A surprise contender for the heavy vacuum engine is the KR-2L if you want a decent TWR

[kStrout]

Just based off of math I can do in my head, to have enough 48-7Ss to equal 1 LV-30, you need 8(or for slightly less thrust: 7). That's a good number, producing 240 kN of thrust, more than the LV, but at just over half the weight, the downside is that it will cost 2,100 well over double that of the LV-30

[RAINCRAFTER]

I'm a 48-7S aholic,,,

Well, I'm an LV-909 lover...

[Jouni]

As you can see the 48-7s is king for some parts, the nuke is king for others and the ION king for a lot of the rest, depending on the desired TWR.

There is also a band, where a single Skipper beats every other combination of a single engine type. The band looks narrow in a logscale graph, but it covers delta-v/TWR/payload ranges that are relevant for launch vehicles. The band should be wider in atmospheric and mixed atmospheric/vacuum charts, and there should also be another band for a single Mainsail.

[SlabGizor117]

Cool, thanks guys! I like having a cluster of 48-7S's too, I haven't done it much yet tho.

[StrandedonEarth]

I just landed a 2-stage Moho lander with 4 48-7S's surrounding an LV-909 on the descent stage. Oodles of TWR to make it easy.

[cantab]

Regarding the above charts, do they take into account the mass of the ion engine's power supply? I suppose technically it can be zero if you spam oxstats on octagonal struts and/or radial batteries, but more practically you're going to be using the extendable panels to keep the part count under control.