Heavy Lifting?

[kiany123]

Im having a bit of truoble figuring out good rocket designs that can lift a fairly heavy payload. Can anyone help me out on this enormous problem?

[Noticeably FAT]

I don't know what you consider "heavy", but this will get 80 tons into orbit. The four nuke engines at the top of the screenshot are sitting under a jumbo tank + orbital maneuvering stuff.

[Pyotor Gagarin]

Is it mostly a structural failure problem? For "telescoping anomalies", I've found that careful placement of a few struts can make a big difference. Try looking at the flight report window after a breakup and see which area failed first. Then try to use struts, or a completely different configuration to relieve some of the pressure on that part of the design. It also helps to keep your acceleration down. Try to stay under two gees for the really big designs. Here's a picture of the struts on my standard heavy lifter: (I might be overdoing it).

If you're still having problems after awhile, maybe you can post a picture and people can tear it apar- *ahem* analyze it for you.

[Akalaël]

A good desing rocket for lifting any playload with the more efficiency involves a desing that is named Asparagus.

In sutch a desing, your rocket is surrounded by multiple tanks+engines, and, as the rockets takes altitude, it separates of those.

Basicaly you have to put fiuel lines from the tanks that will drop off first to the ones that will stay.

Here's my heavy lifter : the center rocket heigh 155 tons :

See those tankers at the radius ? They provides fiuel for all the rocket. When I jettison those, the rest of my tanks are FULL.

And in case of :

http://kerbalspaceprogram.com/stock-enormus-refiuling-and-deep-space-ship/

Edited May 1, 2013 by Akalaël

[Temstar]

A good desing rocket for lifting any playload with the more efficiency involves a desing that is named Asparagus.

This, asparagus staging is the secret to building highly efficient rockets. At its most simple form it consists of three stacks joined together side by side. The two side stacks feed fuel using fuel line into the centre stack. At lift off all three stack's engines fire, the two side stacks continuously pump fuel into the centre stack to keep it fully fuelled. Once the side stacks are empty they are jettisoned and the centre stack, still fully fuel continues on into orbit.

Of course it gets more complicated than that, you can add more pairs and arrange them radially around the centre core to get this kind of thing:

The best way to understand how such an asparagus rocket work is to load one of those Zenith rocket up in the VAB, have a look around then launch one and see how the fuel drains.

[capi3101]

1) Use struts. Be as copious as you need to be in order to keep your stack intact long enough to get it into orbit.

2) Be willing to throttle back. If your design's got more thrust than it needs, too much thrust will cause it to telescope as soon as you do your gravity turn. By the same token, nurse your rocket through the gravity turn; don't do it all in one go.

[cfinerty]

Hi there,

My approach is similar to Akalaël's. One of the largest issues with heavy lifters is that if they are too tall they become bottom heavy as the upper fuel tanks drain this will cause them to be very prone to tumbling in the upper atmosphere.

I would recommend that you start with a short drive section below your payload and then increase the height with each subsequent ring of tanks. This ensures a very stable rocket but does restrict the shape of your payload.

i have an example rocket which can get a 306 ton payload to orbit and is rock steady all the way up which should help illustrate some tips (stock except for mechjeb).

here is the load in the center with 3 asparagus rings around it (the first ring is hidden)

here you can see how the central drive and the first ring are the those with the highest thrust to weight and are directly below the payload allow the lift to be transfered without any nasty shearing forces.

Do not be tempted to start with the tallest in the center and work outwards getting shorter, this would mean that the outermost stacks have the highest thrust to weight and also far greater leverage and therefore are very prone to shearing off and destroying the rocket.

Essentially the central rockets are there to lift the payload all of the other stacks are just self supporting fuel reserves. The tall outer stacks on the rocket are providing almost no lift to the payload until they are almost empty.

You may have noticed that I have used a ring asparagus rather than a spiral. By this i mean that I jettison the entire outer ring at once then the entire next ring and so on. While a spiraling approach where 2 tanks are dropped at a time in a spiral is more efficient I find that the difference is small and i prefer not to have the axis of symmetry of my rocket rotate as it makes it harder to keep on course. I would recommend this approach first as it is also far easier to build and manage.

Finally I would highly recommend mechjeb for super heavy lifters, that rocket has 500+ parts which brings the game to a crawl and makes manual control very hard, using the ascent autopilot which is of course unaffected by the game slowdown has been key.

If you have any specific questions on building lifters just ask .

ps. be wary of mainsail engines they are very prone to wobble, I would suggest locking the gimble on all but the innermost mainsails to help prevent rockets from shaking themselves apart.

pps. I realised I might help if I removed the payload to give a better view

Edited May 1, 2013 by cfinerty

[cfinerty]

-double post-

Edited May 1, 2013 by cfinerty