Crazy Idea - SRB Assist for Interplanetary Ships

[Commander Zoom]

Anybody who's sent a ship to another planet knows that one of the most boring parts of the whole process is the initial burn out of (usually) Kerbin orbit. It's a big long burn, usually done with nuclear engines (efficient, but not that fast, especially when pushing a massive vessel with landers, etc etc) and you're limited to 4x acceleration at most; often, you have to make multiple passes (to take full advantage of the Oberth effect) because it's so long.

Today, as part of answering someone's question about HyperEdit, I was messing around with teleporting a very simple ship (1-kerb capsule with parachute and decoupler on top of a tall SRB) I'd already built for something else into Mun orbit. On a whim, I decided to fire it off, and not only reversed my orbit but achieved escape velocity. Now, of course we're talking about the Mun, and a payload that weighs next to nothing, but it got me thinking...

Has anyone out there tried strapping some SRBs onto your mission to Duna or Jool or wherever, to help give it that starting "kick"? Yes, you're trading efficiency for time, but if efficiency was all we cared about, we'd be mounting only a single nuke engine - or, God help us, ions - and taking a whole RL day. This is about impatience and (depending on who you ask) being "kerbal".

[Francesco]

For a ship that small, a burn to anywhere is going to be very short anyway - no real gain in making it 30 or 45 sec long instead of a couple of minutes or so.

For large payloads, SRB don't provide enough delta-v anyway due to their low ISP.

But yeah, sometimes I do that for fun

[SkipSpikowski]

I have thought about doing this, but I always come back to, "what if something goes wrong?". You can't recover, you're all in. That being said, DO IT.

[magnemoe]

For a ship that small, a burn to anywhere is going to be very short anyway - no real gain in making it 30 or 45 sec long instead of a couple of minutes or so.

For large payloads, SRB don't provide enough delta-v anyway due to their low ISP.

But yeah, sometimes I do that for fun

Pretty much this, your better off using the SRB during liftoff.

[Payload]

I often think about using the ION engines but I actually did use them once to put a satellite around the moon. That took so long I could have devised a fuel truck mission or 20. This idea inspired me to make a small space cycle for Jeb that uses an ion engine with 10 seperatrons as a turbo. Most of the time it puts along like one of those battery powered wheel chairs but Jeb knows that he can hit the boost at any time for a speedy get away.

[Bacterius]

I have thought about doing this, but I always come back to, "what if something goes wrong?". You can't recover, you're all in. That being said, DO IT.

Can't you separate the SRB's prematurely if something goes wrong? It's quite safe to do so in open space (in the atmosphere they tend to smash back into your craft)

EDIT: if they are radially attached, obviously. If you've got them at the back of your ship you're boned.

[Kowbell]

I have thought about doing this, but I always come back to, "what if something goes wrong?". You can't recover, you're all in. That being said, DO IT.

No, you could attach the SRB's with radial decouplers and perhaps I-beams.

[TheHengeProphet]

For those who watched the end of the stream marathon with Spooty, this is exactly what he did on his mission to jool!

[DerekL1963]

Has anyone out there tried strapping some SRBs onto your mission to Duna or Jool or wherever, to help give it that starting "kick"? Yes, you're trading efficiency for time, but if efficiency was all we cared about, we'd be mounting only a single nuke engine - or, God help us, ions - and taking a whole RL day. This is about impatience and (depending on who you ask) being "kerbal".

I've build a tug that had a mix of LV-N's and LV-T45's, it worked well enough when using the -T45's for quick kicks.. Only it was easy to get addicted to the extra thrust and thus waste the efficiency of the -N's.

[Jarnis]

SRBs suck. Low ISP. Once in orbit, TWR is irrelevant.

What we do need is a way to program burns... there are addons for that (heck, mechjeb can fly a planned burn) but the base game could really really use an "auto cutoff" so you don't have to hover over the keyboard over long interplanetary transfer burns. Once the trajectory is planned and you have the maneuver node (and are pointing at it), there should be a way to just execute that at T-0

[ComradeGoat]

Why not use a liquid fuel droptank with a high thrust engine on it, and then jettison it when the tank is empty? Better ISP than an SRB, same benefits, can be switched off and gives you extra fuel for your destination if you don't use it all on the initial "kick".

[Commander Zoom]

Indeed, something along those lines is what I've been contemplating (after further consideration, and reading the previous posts in this thread).

[Carthaginian]

EDIT: if they are radially attached, obviously. If you've got them at the back of your ship you're boned.

Then attach them as an 'escape tower' type feature.

Then, you are not likely to be boned at all... and could even bone that offensive Mun crater in the process...

[Tommygun]

Well the idea is not that different from the Payload Assist Module (PAM).

I think the real challenge is trying to guide it with enough precision for planetary transfer.

[Sean Mirrsen]

I haven't used them on interplanetary transfers yet, but my first experimental series of Kethane miners was a converted space tug, and it needed an extra kick to get into orbit because of all the extra mass... so I just slapped four small SRBs on the pusher stage.

With predictable effects on Jeb.

They otherwise worked quite fine, however.

[boolybooly]

Not that SRBs are not fun and would come into their own if they were cheap in an economic sim or exploded with pretty colors when they were done, but if your priority is patience or lack thereof why mess about with SRBs when you have mainsail? Just launch up triple stack 1+2 with mainsails outer pair and an array of quad Ts under the inner stack, refuel in LKO and blow it all in one mad short burn, liquid has better dv per mass anyway, about 30% better.

[Francesco]

Well the idea is not that different from the Payload Assist Module (PAM).

Yes, and that's exactly what I'd like to see added in the future, speaking of new parts: more solid boosters.

Especially with longer burn times (90-120 seconds, let's say), in both 1.25m and 2.5m sizes.

[Motokid600]

Why not use a liquid fuel droptank with a high thrust engine on it, and then jettison it when the tank is empty? Better ISP than an SRB, same benefits, can be switched off and gives you extra fuel for your destination if you don't use it all on the initial "kick".

This. Do it Apollo style. Use the 3rd stage of your launch rocket for the ejection burn.

[Lundmunchkins]

SRBs suck. Low ISP. Once in orbit, TWR is irrelevant.

What we do need is a way to program burns... there are addons for that (heck, mechjeb can fly a planned burn) but the base game could really really use an "auto cutoff" so you don't have to hover over the keyboard over long interplanetary transfer burns. Once the trajectory is planned and you have the maneuver node (and are pointing at it), there should be a way to just execute that at T-0

That is basicly autopilot, something squad won't implement Edited October 16, 2013 by Lundmunchkins
fixed vocab

[SRV Ron]

Yes, and that's exactly what I'd like to see added in the future, speaking of new parts: more solid boosters.

Especially with longer burn times (90-120 seconds, let's say), in both 1.25m and 2.5m sizes.

Try the NovaPunch mods. There is a variety of SRB to play with from minis to big powerful 2.5 meter ones and a long burn one. But, as usual, they are only suitable for use during the launch phase.

Long burn booster used to test the NASA Minotaur design;

[Francesco]

Try the NovaPunch mods. There is a variety of SRB to play with from minis to big powerful 2.5 meter ones and a long burn one. But, as usual, they are only suitable for use during the launch phase.

Long burn booster used to test the NASA Minotaur design;

how long does that burn for?

[SRV Ron]

how long does that burn for?

I believe about twice the normal large booster. Enough to start the orbital turn. You can tell how long it is from where the yellow striped decoupler is located for the small liquid fuel stage. Still, the liquid fueled version is far more efficient in sending the probe to low Mun orbit. Like the real NASA mission, the thruster pack on the probe is used for final low Mun insertion.

[ouion]

In real life some Prodes use solid motors to propelled them to the moon,but i am not sure about interplanetary missions.