Why doesn't Nasa, Space X etc use heavy lift rockets that carry multiple payloads into orbit?

[rkman]

I'm having trouble picturing this in my mind, if one rocket can get to space on its own, why can't multiple rockets that are effectively just flying very close together?

Same reason why NASA build a Saturn V instead of bundling a couple of Atlas rockets.

Of course, you might be able get some aerodynamic advantage out of the fact that you are launching all of them at once by stacking them on top of each other, but that works in favor of one large rocket rather than against it.

If it wasn't for the square cube rule.

[TeeGee]

Nobody is putting constellations of large satellites into LEO, and LEO payload figures are in most cases a red herring. Delta IVH can put 14 tons into GSO, which would be just under 3 large modern comsats. The go-to launcher for putting something about 5 tons GTO alone would be proton, at about $70 million per launch; whereas Delta IVH is somewhere in the region of $400 million.

Also, that's not how pounds and tons work.

http://www.convertunits.com/from/lb/to/tons

http://en.wikipedia.org/wiki/Delta_IV_Heavy

[Kryten]

Hint: people can see when you've edited something.

[cantab]

I'm having trouble picturing this in my mind, if one rocket can get to space on its own, why can't multiple rockets that are effectively just flying very close together?

A rocket that's relatively squat can have stability issues, they need to be sufficiently slender to fly straight or else you need to add over-large fins and they add their own mass and drag.

At least that's how it behaves in FAR.

[magnemoe]

Trying to get multiple large payloads for any deep space destination at current demand is an exercise in futility, and with the current state of the SSO/LEO market it would be pretty close. D-IVH isn't going to be able to put up station resupply missions this way due to waiting for other payloads inevitably messing up the scheduling, Russian or Chinese government sats aren't going on one before hell freezes over. Launch of NGSO communications satellites like Iridium or Globalstar are also non-starters; it wouldn't be possible to launch more than one plane at a time, and even for the large Iridium sats a single plane is well within the capability of Proton.

That leaves you with the commercial remote sensing market, which isn't much; the average mass of a satellite in this class is well south of a ton, and there are only a few launches a year even with current launchers. You'd have to wait decades to fill something like a D IVH.

yes, for smaller stuff where you only want up in space secondary payload works nice, lots of standard satellites like GPS are launched into various orbits making it hard to bundle.

Larger rockets tend to be more expensive as they are used less, note this might chance with more modular designs.

As I remember it was one falcon 9 launch who released a lot of small satellites.

This brings up Musk's small internet satellites, they is planned to be small but go in various obits so I wonder how he plan to launch them? bring back falcon 1?

[Brotoro]

For the same reason I drive my car from home to work rather than trying to coordinate a whole van load of people who want to go to their jobs. Sure, it might be more energy efficient...but it's too much of a bother.

[Kryten]

This brings up Musk's small internet satellites, they is planned to be small but go in various obits so I wonder how he plan to launch them? bring back falcon 1?

Falcon 9 for planes, and I think they were looking at LauncherOne for single-sat replenishment.

[cpast]

When you talk about "different altitudes," that's KSP concepts talking. In real life, in the vast majority of cases, altitude isn't the only (or even the primary) concern about your orbit -- you also care about orientation of the orbit (argument of periapsis, longitude of the ascending node, inclination). In KSP, unless there's a reason not to, you always launch into equatorial orbit. Equatorial orbit is a fine orbit, which is generally quite nice. But no launch sites are on the equator in real life, so you have to launch into an inclined orbit (GTO loses its inclination at apogee, at the same time as the satellite enters GEO). Almost all satellites are intended to achieve some goal on Earth, in which case you care very much about what your satellite's ground track will look like. For instance, if you launch a constellation of satellites, you have fairly specific requirements for orbital orientation, and it's not enough to be high enough.If you're going to a space station you have to match its orbit, which is going to not be in GEO (so a GTO satellite won't easily mix with it -- you *could* do it if the satellite itself went from LEO to GTO, but that's worse than having the launch vehicle deliver straight to GTO). And then you have to deal with the massive amount of integration work, knowing that if *any* satellite fails it could cause serious problems for the rest.

Lots of payloads doesn't really work unless you don't particularly care what orbit most of them go into. It's complicated to deal with, and so you *would* wind up in the same situation as someone using a semi to handle mail delivery routes.

[Beowolf]

I'm having trouble picturing this in my mind, if one rocket can get to space on its own, why can't multiple rockets that are effectively just flying very close together?

One problem with "multiple rockets...flying very close together" is the atmospheric shock wave. Picture the cone-shaped shock wave coming off the highest point of a rocket. If any other parts of the rocket, like large side boosters, stick through that cone, air resistance goes up hugely, making it difficult to keep accelerating, and producing stresses that can easily rip your vehicle apart. In aircraft design, this is known as area rule. Several 1950s fighters were terrible underperformers until we figured out what was going on.

Slower aircraft can't casually fly close together either. Even below mach 1, the airflows interfere with one another, causing little areas of extra lift or no lift moving over the wings. Close formation flying's a significant skill for pilots, and even after years of training and practice, the constantly changing conditions cause occasional

. Edited February 25, 2015 by Beowolf

[FishInferno]