The Thud - an underrated launcher engine?

[Mastikator]

3 hours ago, Alshain said:

So I decided to try a little empricial testing on what I believed the numbers were telling me from my earlier posts and in the end I believe I was correct, I could not build a Rocket capable of orbit using the Thud cheaper than an equivalent payload rocket using a Swivel and SRB's (specifically Hammers).  I did come really really close however, within a few hundred funds. Now I am not perfect by any means, so here is a picture of my rocket including cost and if anyone can build a cheaper rocket using Thuds I would be very curious to see it. This is a 2 ton (2.040 precisely) payload lifter aimed at 100km orbit and I wanted to keep it around 1.5 TWR on the launchpad, I used ore and parachutes to simulate payload.  Of course none of this matters if cost is not your concern, but it's still something to consider.

 

A hammer costs 400, radial decouplers cost 600. You can put a stack decoupler below the swivel and have 3 hammers below and save 200 funds.

[Alshain]

27 minutes ago, Mastikator said:

A hammer costs 400, radial decouplers cost 600. You can put a stack decoupler below the swivel and have 3 hammers below and save 200 funds.

Except you can't control it.  Besides, that's not what I was asking for.  I was asking if anyone could make a cheaper thud based lifter.

Edited May 11, 2016 by Alshain

[suicidejunkie]

39 minutes ago, Mastikator said:

A hammer costs 400, radial decouplers cost 600. You can put a stack decoupler below the swivel and have 3 hammers below and save 200 funds.

This is exactly my Bag-O-Hammers design style.  For heavy lifting, a grid of 12+ hammers mounted on one stack decoupler can really give you a great start for very few funds.

Control isn't an issue if you use symmetry and just let the hammers give you some vertical starting speed.  Then stage 'em off and use the regular control systems on your launch vehicle to start the gravity turn.

[LordKael]

26 minutes ago, Alshain said:

Except you can't control it.  Besides, that's not what I was asking for.  I was asking if anyone could make a cheaper thud based lifter.

You've raised a lot of really good points about the Thud being a less-than-economical option on the pad, but I'm not sure that that is it's intended use.

For example: I use them for small stages to get payloads from a cargo bay into a higher orbit; the radial attachment allows me to maximize my cargobay space. Now, I know the thread is supposed to be about using the Thud on a launcher, so here's my two cents:

Building a launcher that isn't perfectly efficient in the first stage isn't a huge deal. The first stage is primarily fuel weight anyways, so if you lose a dozen or so dV for aesthetics, who cares? Secondly, using them to offer gimbal on the higher thrust, but gimbal-less Reliant engine (1.25m) is a great way to boost TWR and save on the control surface fins. 

[Alshain]

19 minutes ago, LordKael said:

You've raised a lot of really good points about the Thud being a less-than-economical option on the pad, but I'm not sure that that is it's intended use.

For example: I use them for small stages to get payloads from a cargo bay into a higher orbit; the radial attachment allows me to maximize my cargobay space.

Well of course, I use them plenty in space, especially on landers, but that isn't the thread topic.

[moogoob]

Thanks for your investigation, @Alshain! The biggest thing I get from that is that while no, they're not AS efficient as a good Swivel and SRB setup, they are more efficient than many give them credit for.

16 hours ago, suicidejunkie said:

This is exactly my Bag-O-Hammers design style.  For heavy lifting, a grid of 12+ hammers mounted on one stack decoupler can really give you a great start for very few funds.

Control isn't an issue if you use symmetry and just let the hammers give you some vertical starting speed.  Then stage 'em off and use the regular control systems on your launch vehicle to start the gravity turn.

I call this the HALP- High Altitude Launch Pad. Mostly for the acronym. Trouble spacing your cargo? Get some HALP today!

[Alshain]

Well I'm still playing with these on a lifter, from the cost perspective of course, and I actually found a niche for them in my 35 ton lifter that saves about 2 grand.  The previous lifter used a Skipper upper stage, but I swapped it out for 2 thuds and a poodle.  Used almost exactly the same fuel to get to orbit, but was cheaper.  Looks like that trick may work on my 40 ton as well but I'm still testing it.  It may actually replace the skipper as an upper stage entirely.

Edited May 11, 2016 by Alshain

[James Kerman]

They are useful in bamboo/train staging .  The core stack fuel tanks essentially become drop tanks.

[maccollo]

On 5/11/2016 at 11:41 PM, Alshain said:

Well I'm still playing with these on a lifter, from the cost perspective of course, and I actually found a niche for them in my 35 ton lifter that saves about 2 grand.  The previous lifter used a Skipper upper stage, but I swapped it out for 2 thuds and a poodle.  Used almost exactly the same fuel to get to orbit, but was cheaper.  Looks like that trick may work on my 40 ton as well but I'm still testing it.  It may actually replace the skipper as an upper stage entirely.

But the poodle has enough TWR without the thuds, and can get to orbit for a little less than 3300 m/s. By using the thuds on the upper stage you are reducing performance, and making it more expensive.
The only cost effective application that I have found for the thuds is when they are used as verniers with an otherwise all kickback first stage. To make such a first stage work otherwise would require lots of reaction wheels or fins, which don't provide thrust. While cost/performance of the thud isn't great, it's not awful, and their relatively high gimbal range means that it's pretty well suited for the task.

Edited May 13, 2016 by maccollo

[Alshain]

2 hours ago, maccollo said:

But the poodle has enough TWR without the thuds, and can get to orbit for a little less than 3300 m/s. By using the thuds on the upper stage you are reducing performance, and making it more expensive.
The only cost effective application that I have found for the thuds is when they are used as verniers with an otherwise all kickback first stage. To make such a first stage work otherwise would require lots of reaction wheels or fins, which don't provide thrust. While cost/performance of the thud isn't great, it's not awful, and their relatively high gimbal range means that it's pretty well suited for the task.

The poodle does not have enough TWR.  Not at that range.  I use the poodle by itself on the 30 ton lifter, anything more and I have to use either a skipper or augment the poodle.

[maccollo]

53 minutes ago, Alshain said:

The poodle does not have enough TWR.  Not at that range.  I use the poodle by itself on the 30 ton lifter, anything more and I have to use either a skipper or augment the poodle.

It definitely has enough TWR, even at 40 tons of payload instead of 35.

 

Edited May 13, 2016 by maccollo

[Alshain]

2 hours ago, maccollo said:

It definitely has enough TWR, even at 40 tons of payload instead of 35.

Apples and oranges, my lifters all go to 100 km, you just barely made orbit.  You would have to add even more fuel, which would only lower your TWR.

Edited May 14, 2016 by Alshain

[maccollo]

14 hours ago, Alshain said:

Apples and oranges, my lifters all go to 100 km, you just barely made orbit.  You would have to add even more fuel, which would only lower your TWR.

More fuel is not necessary. Going to 100 km from the orbit that I ended up in takes 37 m/s. With a better executed launch it can get to 100 km x 100 km with 70 m/s to spare, and it it was carrying 14% more payload mass than yours. Your rocket was only carrying 35 tons and you are saying the poodle upper stage has insufficient thrust on it's own, but it clearly does.

Edited May 14, 2016 by maccollo

[Belerafon]

On 5/8/2016 at 6:39 PM, Dispatcher said:

I've used Thuds on small SSTOs.  Recall that the iSP remains the same, but the thrust is multiplied by the number of units {radially attached in this case).  I think they perform better since 1.1 than previously.

Edit:  since their being remodeled, they look cool too.

 

Aaaaaand they look much more 'ghetto.'

The good ol' kerbal style engines!

[Curveball Anders]

I sometimes slap two Thuds to help an overloaded Skipper before Mainsail is unlocked.

[Belerafon]

On May 10, 2016 at 0:50 AM, sgt_flyer said:

the Thuds allow for very pretty engine clusters, that can neatly fit within a 1.25m package

 

I squeeze them into F9 boosters.

[FirstSecondThird]

I don't really give two s**ts (excuse my language) about using SRBs or LFO engines for my rockets. As long as it's cost ineffective, fuel efficient, and capable of lifting it's payload, I'll build it. But anything outside of those criteria for my rockets is out of the question and I will not, repeat WILL NOT, build rockets of that sort, although, in Sandbox, I could care so much less. So, layman's terms, now that I got my big mouth to stop talking, I will build rockets that are worth the price and does it's job efficiently and powerfully, but only rockets of that sort.

On 5/10/2016 at 0:50 AM, sgt_flyer said:

the Thuds allow for very pretty engine clusters, that can neatly fit within a 1.25m package

 

That is one sexy Soyuz clone.

[Moesly_Armlis]

On 5/12/2016 at 0:44 AM, James Kerman said:

They are useful in bamboo/train staging .  The core stack fuel tanks essentially become drop tanks.

Thuds and drop tanks were the most efficient lifter concept for careers that had 10% difficulty sliders.  With vessel and VAB/SPH limitations two Thuds could lift the 18 tonne vessel.

The vessel was designed to lift a fuel tank that would dock to an orbiting Mun/Minmus lander.  Sometimes the drop drop tanks would survive the fall and be scattered around the launch pad.  The vessel was then named the Litterbug lifter.

edit: after reviewing the video I realized the Part Action Groups gave me trouble.  Now the Part Action menus can be pinned and decouplers can be set to enable crossfeed.

Edited May 17, 2016 by MoeslyArmlis

[Alshain]

12 minutes ago, MoeslyArmlis said:

With vessel and VAB/SPH limitations two Thuds could lift the 18 tonne vessel.

Sorry, but I'm not buying that one.  18 tonne payload with 2 thuds and an FL-T100 has a thrust to weight ratio of 1.08.  Perhaps you aren't remembering right, but I don't see how that scenario is mathematically possible.

Edited May 17, 2016 by Alshain

[Moesly_Armlis]

3 minutes ago, Alshain said:

Sorry, but I'm not buying that one.  18 tonne payload with 2 thuds and an FL-T100 has a thrust to weight ratio of 1.08.  Perhaps you aren't remembering right, but I don't see how that scenario is mathematically possible.

That low TWR was the reason for the drop tanks.  Also had to set the gimbal to off for the first part of the launch.

 

Edited May 17, 2016 by MoeslyArmlis

[Alshain]

@MoeslyArmlis That is an 18 ton vessel, sorry I misunderstood, I thought you meant 18 ton payload.  My fault.

[Moesly_Armlis]

Just now, Alshain said:

@MoeslyArmlis That is an 18 ton vessel, sorry I misunderstood, I thought you meant 18 ton payload.  My fault.

No problem.  But I did not remember correctly.  This video shows the launch of the orbiting lander and then another Litterbug lifter was used to deliver the fuel.