Why do people dislike developing an HLV?

[Shadow Addict]

I'm not a strict supporter of developing an HLV, but why exactly do some people see it as unnecessary? I know that Chris Kraft himself said the idea was bad, and I'd trust his judgment, so could somebody explain to me why it's not a good idea?

 

[Urwumpe]

I'm not a strict supporter of developing an HLV, but why exactly do some people see it as unnecessary? I know that Chris Kraft himself said the idea was bad, and I'd trust his judgment, so could somebody explain to me why it's not a good idea?

It is just a brute force solution, that costs extremely much money for the tiny advantage that the technological risk of on-orbit assembly is delayed for further into the future.

There is no such thing as a Big Dumb Booster, that is cheaper than the equivalent in medium launch vehicles, the fixed costs for ground infrastructure for a heavy launcher is always much bigger as the costs for a medium launcher, and a medium launcher reaches a higher flight rate for the same costs. It is far cheaper to test and operate a medium launcher, and a medium launcher can easier be sold to commercial customers.

A Big Dumb Booster is practically just a Big Dumb HLV, with all disadvantages of an HLV exaggerated while fixing some problems of a medium launcher.

 

[Andy44]

An HLV would make sense if you were going to have a high launch rate. In the Saturn days, they were launching a Saturn V like once or twice a year, and in the months in between they had to pay for all the support staff and facilities, the "fixed costs", which makes it very expensive. The rockets themselves have a high unit cost as well.

Compare that with something like the Delta II, which launches much more often, since most space missions don't have a huge payload mass. You are paying people to work on the project, but they're not sitting around for months or years between launches, they're actually launching paying cutomers' payloads fairly regularly.

Of course, since nothing NASA does actually makes money, the decision to build an HLV really depends on how much money you want to waste. If you are building a gigantic 2001-style moonbase, with frequent high-mass launches, then an HLV "makes sense", since in the greater scheme you are wasting most of your money on the moonbase project rather than on the launch vehicle.

 

[Sky Captain]

What about strapping together multiple first stages from a medium laucher to form a backbone of HLV when there is some odd payload that`s heavy and can`t be easily broken down into tiny modules? Suppose you take 7 first stages from Zenit rocket and strap them together in 1 in core six around fashion to make a nice HLV. That way you can use the same assembly line and same personal you normaly use for building and launching your medium rockets to cut down costs. It would be less efficient than dedicated HLV of the same capacity designed from scratch, but likely much more cheaper because it shares common components with your frequently used medium launch vehicle.

 

[Urwumpe]

What about strapping together multiple first stages from a medium laucher to form a backbone of HLV when there is some odd payload that`s heavy and can`t be easily broken down into tiny modules? Suppose you take 7 first stages from Zenit rocket and strap them together in 1 in core six around fashion to make a nice HLV. That way you can use the same assembly line and same personal you normaly use for building and launching your medium rockets to cut down costs. It would be less efficient than dedicated HLV of the same capacity designed from scratch, but likely much more cheaper because it shares common components with your frequently used medium launch vehicle.

That works in Velcro Rockets, but not in reality. For clustering stages around a core, you need structural supports and design the rocket/ground equipment for it in advance.

 

[T.Neo]

I don't see why a launcher could not be built out of multiple common boosters as a matter of course.

It would result in a large host of engineering issues though.

 

[Sky Captain]

That works in Velcro Rockets, but not in reality. For clustering stages around a core, you need structural supports and design the rocket/ground equipment for it in advance.

Well, then how would costs go designing from ground up a heavy rocket that`s only this big vs designing a medium rocket that can be scaled up according to payload via clustering

At least the Russian Angara rocket family which is in dewelopment now employs the concept of strapping together 3 - 7 universal rocket modules so the concept has to have some advantages.

 

[Urwumpe]

Well, then how would costs go designing from ground up a heavy rocket that`s only this big vs designing a medium rocket that can be scaled up according to payload via clustering

At least the Russian Angara rocket family which is in dewelopment now employs the concept of strapping together 3 - 7 universal rocket modules so the concept has to have some advantages.

Yes, and as you can see in the Angara, you actually pay mostly for the development of the heaviest configuration, and then have the chance to use it with smaller configurations and a little payload penalty to more optimized launchers.

 

[T.Neo]

But it can still be used as a medium scale launcher that allows for expansion as a heavier vehicle if the need ever arises.

 

[Sky Captain]

Yes, and as you can see in the Angara, you actually pay mostly for the development of the heaviest configuration, and then have the chance to use it with smaller configurations and a little payload penalty to more optimized launchers.

Yeah, but once R&D is paid you got whole family of rockets that can be used for variety of payloads. Even if 90 % of your flights are 1 or 3 core versions with heavy configuration flying only few times a year there has to be a cost savings overall at least because your factory that makes cores and personel are used more efficiently. With fixed size heavy rocket that flies few times a year you have a personal and factory doing nothing for most of the time.

 

[Zatnikitelman]

Like the DeltaIV and Atlas V...

 

[2552]

It's simple. Low fixed-cost, high flight rate launchers (medium lift) are more cost-effective than high fixed-cost, low flight-rate launchers (HLV) for the same total payload.

Like the DeltaIV and Atlas V...

Because they aren't being used as much as it was thought they would, and because they are two different launchers, so they can't leverage each other's flight rate. With the planned Common Centaur upper stage, and eventually ACES, they can share some costs though. And if this was the new NASA Exploration plan, Atlas V and Delta IV would have a much higher flight rate. Would be cool to have that as an Orbiter addon.

 

[Urwumpe]

That one looks at least more well-thought than the constellation architecture.

 

[tblaxland]

Yeah, but once R&D is paid you got whole family of rockets that can be used for variety of payloads. Even if 90 % of your flights are 1 or 3 core versions with heavy configuration flying only few times a year there has to be a cost savings overall at least because your factory that makes cores and personel are used more efficiently. With fixed size heavy rocket that flies few times a year you have a personal and factory doing nothing for most of the time.

Look at it another way. For 50% (for example) of the development cost, you could cover 90% of launches. Instead of developing the 5-core version for the remaining 10% of launches, you could use the left over 50% of development cost (or less, hopefully) for solving the problems that you thought you needed the 5-core version for (eg, figuring our how to do better on-orbit assembly).

 

[T.Neo]

solving the problems that you thought you needed the 5-core version for (eg, figuring our how to do better on-orbit assembly).

But not the things that only the 5-core version can do, should the situation arise.

 

[Sky Captain]

One advantage HLV has is larger diameter and longer payload fairing which makes things much easier when you for example want to build serious interplanetary mission. A missions to Moon and NEO`s could be supported by current EELV`s if propellant depots are used, but what about Mars? Most plans call for surface stays for over a year so you need some serious habitation module that can enter Martian atmosphere and land. Can such a module be made of small pieces launched by medium rockets without sacrificing reliability or making costs exploding out of control?

Another heavy payload that comes to mind is nuclear reactors to power electric propulsion. A fast Mars mission needs ~200 MW of electrical power. Larger nuclear reactors tend to be more efficient than smaller ones when it comes to power to weight ratio so it would be advantageous to have 2 - 3 large reactors than dozens of small ones supplying needed 200 MW. A mission to asteorid belt may require even more electrical power to cut down time crew spends in transit.

 

[N_Molson]

According to Astronautix, it is possible to cluster 7 Common Boosters Cores on the Delta IV. With a modified upper stage, you get an HLV (85t to LEO).

But you need a new launchpad, of course.

Proposed upgrade to Delta IV Heavy by clustering seven common booster modules, using a new RS-800K engine in the booster stages, an AUS-60 upper stage powered by 4 MB-60 or RL-60 27 tonne thrust Lox/LH2 engines, and aluminium-lithium lightweight alloy in place of the existing aluminium in all stages. Payload fairings over 6.5 m diameter could be accomodated. Introduction would require new launch pads and booster assembly infrastructure.

LEO Payload: 85,000 kg (187,000 lb). to: 407 km Orbit. at: 28.50 degrees. Payload: 32,000 kg (70,000 lb). to a: earth escape trajectory. Core Diameter: 5.00 m (16.40 ft). Total Length: 67.00 m (219.00 ft). Span: 15.00 m (49.00 ft)

And I think that if the CBCs were buit in great quantities, the costs would drop... This kind of modular architecture is very very smart !

 

[Urwumpe]

One advantage HLV has is larger diameter and longer payload fairing which makes things much easier when you for example want to build serious interplanetary mission.

Strangely, we can build serious houses with trucks, that can only transport a much smaller envelope. And it does not seem much easier to build complete houses in a factory far away and transport the houses to their location.

Sorry, but you are following a fallacy - larger monolithic payloads are never automatically simpler. They are actually even slowing you down after the first three or four launches. If you assemble the spacecraft in orbit from standard modules, you can include improvements and fixes faster than in a monolithic spacecraft that is assembled for years on Earth and has huge R&D programs involved. Only because you can launch it in one piece, it is not less complex. No spacecraft is 400 tons of pure solid metal.

 

[Sky Captain]

Strangely, we can build serious houses with trucks, that can only transport a much smaller envelope. And it does not seem much easier to build complete houses in a factory far away and transport the houses to their location.

Doing equivalent in space would mean either developing robots that can build your ship or accept many many eva hours which would expose astronauts to risk of being hit by some random junk flying in LEO.

 

[Urwumpe]

Doing equivalent in space would mean either developing robots that can build your ship or accept many many eva hours which would expose astronauts to risk of being hit by some random junk flying in LEO.

The chance is higher to be hit by lightning while working on a house on Earth. Sorry, but this is a very weak argument. You risk far more people on the ground, who have to work near your huge rocket, to be killed in a rocket explosion, and want to talk about risks during EVAs.

I don't know how many man-hours we today have spend outside the spacecraft, it should be well in the thousands now, and no astronaut ever got even just injured by space debris. The risk is there, but it is by such "measurements" not higher than the pure mathematical risk calculated by debris models for debris to pass through an astronaut sized area.

And that number is not very huge: Even in Low Earth Orbit, which is quite dirty, you would need to spend many months outside on the average before you would be hit by a piece of debris large enough to damage your suit.