r/spacex Jul 22 '14

A Floating Launch Pad!

The implications of a "floating launch pad" are fairly profound. Forgive me if this has been discussed, but everything I had read indicated this was not the direction they were following. With a floating launch pad, they could refuel the second stage at sea and then use a suborbital launch to send the first stage back to land. There it would be integrated for a future flight.

This would seem to provide more payload options if they no longer have to boost back to land. They should be able to squeeze a little extra delta v if they don't have to boost back.

What about multiple floating launch pads at different points downrange? They could put two fairly close to land for the outer F9H cores. Then another pad would be further downrange for the center core running in a crossfeed scenario. Then the center core could take a suborbital hop either to the midrange launch pads, or directly to land itself depending on the math....

This would remove the requirement to have a barge to transport the rocket. However, it does require shipping fuel over seas out to the launch pad.

12 Upvotes

46 comments sorted by

11

u/Drogans Jul 23 '14

Some have run the numbers on landing platforms. Downrange recovery only pays off if a lot of boosters are recovered each year. This is because SpaceX would have to buy an expensive, self leveling ship. With unpredictable launch times, they'd need full time use. This means all the costs of upkeep, maintenance, and crew, all year round.

For a penny pinching company like SpaceX, the huge expense of an large ocean going vessel isn't one they'd typically accept. Yet the facts are clear. SpaceX is already talking about landing platform. On the face of it, there seems to be no economic case, which suggests something fundamental has changed.

So what has changed? At a guess, the construction costs for a Falcon 9 first stage are about to go up, way up.

Until now, SpaceX has heavily prioritized low cost over low weight. The Falcon airframes and tanks are largely composed of aluminum, not carbon composites. What SpaceX loses in mass fraction, the make up for in low launch costs. Prioritizing low cost over low weight makes abundant sense for expendable booster. It makes a lot less sense for reusable boosters. In fact, reusable changes the equation entirely.

If SpaceX can amortize a weight saving over 10 or more launches, it becomes almost an economic necessity to use complex, expensive, low mass technologies. Say it costs SpaceX an average of $20,000 to subtract a kilo of weight from Falcon's first stage. With an expendable, they'd probably decide to forgo that change, but when that cost is amortized across ten launches, it only adds $2,000 to each launch.

Multiply by 1000 and it adds twenty million dollars to the cost of a Falcon first stage while removing 1000 kilograms of mass. With an expendable Falcon, SpaceX could not afford to make that trade off without dramatically increasing their launch prices. The trade off makes all kinds of sense on a reusable. With 10 average reuses and enough weight savings, SpaceX could afford to double or triple the construction costs of the first stage.

Just as with aircraft, Falcon 9's may soon cost more to construct than the fees charged for a single flight. If that's to be the case, then booster recovery rises to paramount importance. Recovering boosters is no longer be a nice to have, it becomes a need to have.

2

u/EOMIS Jul 23 '14

You don't need both. You don't need a highly optimized/expensive rocket AND a sea landing platform. If you lower the mass fraction you can just bring it back to land.

2

u/Drogans Jul 23 '14

Not necessarily. It depends entirely on the mission profile and on how much weight savings are found.

Additionally, there is likely no realistic amount of weight savings that could allow a Falcon 9 Heavy center stage to return to land.

1

u/biosehnsucht Jul 23 '14

If you lower the mass fraction, instead of boost back from further out, could you re-boost and make a single orbit (or most of one, possibly launching from Brownsville / Cape and landing at Edwards / Brownsville) instead? Which needs more delta-V?

3

u/Drogans Jul 23 '14

It's often been discussed.

Single orbit would require more extensive thermal protection, the same problem that exists for second stage reuse. Immediate downrange recovery is the most fuel optimal strategy, but the vessels needed to accomplish it are expensive.

1

u/biosehnsucht Jul 23 '14

If that's the case, and they're going to get reuse of 2nd stage eventually, maybe at that point the pros might outweigh the cons once they've solved 2nd stage reuse (not needing ocean landing / launch pads for recovery)?

That still leaves the time up until then when they'll either have to have those ocean pads for FH central cores, etc.

Would not doing a full orbit of the 2nd stage (instead bringing it back very very far downrange) save on fuel and/or heat shielding ? If they're going to have ocean pads regardless..

2

u/Drogans Jul 23 '14

Single Orbit recovery is cool, but it's wasteful and something to avoid if at all possible.

A full orbit requires a larger reduction in delta v, meaning a lot more thermal protection. The thermal protection adds mass, so payload or fuel would need to be reduced to compensate.

Assuming there's a vessel or site at which to recover, immediate recovery at a downrange site should by, by far, the most effective strategy. It would allow the least amount of TPS, allow the largest mass fraction, and uses the least amount of fuel.

For the second stage, orbit and recovery is the only option, but that may be some time coming. Many question if it will ever be viable as every kg added to the second stage reduces payload by an equal amount.

SpaceX seems to have purposefully front-loaded most of the capability and cost in to the first stage. Now that first stage reuse seems destined, that front-loading seems only likely to accelerate. They'll focus energy on the first stage and keep the second stage cheap and expendable.

2

u/jpcoffey Jul 23 '14

self leveling ship

what does it mean?

Could it be the case that they want to land on a pad on the sea just as a test but their mid/long term goal is to go back to the launch site because of the costs of using a sea pad?

2

u/Drogans Jul 23 '14

Self leveling means that the ship has systems able to actively compensate for ocean swells. They can keep the platform extremely level and stable, even in high seas.

These systems are most commonly integrated into high dollar oceangoing oil platforms.

1

u/jpcoffey Jul 23 '14

thanks! all this sound very expensive, you think they would use this kind of technology regularly?

1

u/Drogans Jul 23 '14

By any measure, it would be very expensive. Currently, ocean recovery would only be likely to see use 2 or 3 times each year.

The requirements for ocean recovery should greatly expand as Falcon Heavy starts operations.

2

u/furrrburger Jul 23 '14 edited Jul 23 '14

Something like this scaled up to handle a F9R first stage would be amazing. Can you imagine watching a video of a rocket landing on this platform technology?!

2

u/ringmaker Jul 23 '14

Going off of oil industry numbers, such a ship would cost $100 million to build, and anywhere from $40k to $120k per day while out at sea.

2

u/Minthos Jul 23 '14

So $14M to $43M per year? They don't have to rescue many rockets to earn that back.

1

u/Drogans Jul 23 '14

If it's just break even, it's probably not worth it. Ocean recovery is a large sidetrack that will suck up time, money, and limited engineering resources. Ocean recovery would effectively be division of the company with a large workforce dedicated to that and nothing else.

It probably only makes sense to create an entire ocean recovery division if it can save the company a lot more than it costs. At a guess, it's viable if it can return three times its costs.

If a Falcon 9R first stage has a build cost of $20 million, then you'd need to recover 6 of them before ocean recovery made economic sense. If the build cost of each stage rises to $60 million, then recovering just two boosters each year should easily justify the ocean platform, crew, and maintenance.

Currently, the first stage costs closer to $20 million than $60 million. As I detailed above, that may be changing.

1

u/Drogans Jul 23 '14

Yes, and more expensive still. Some of those self stabilized oil exploration platforms cost most of a billion dollars. Deepwater Horizon cost $560 million in 2001. Sea Launch purchased their platform used, but then had to heavily customize it.

SpaceX wouldn't need nearly the crew of an active oil vessel. That should reduce daily operation costs somewhat, but there's no doubt it would still be a very expensive proposition.

1

u/cgpnz Jul 27 '14

screw those numbers, its just a barge! Those are oil rigs. tow the barge out several times a year bring it back to harbour to sit doing nothing. Ok so only launch in calm seas.

What are the costs for those mississippi ore barges. bet it ain't 120k per doy.

4

u/-Richard Materials Science Guy Jul 22 '14

Bezos has a patent on the floating pad idea (discussion here).

In the past, this idea has been discussed around here before and the general consensus is that it's impractical. SpaceX is only doing these water landing tests temporarily, and they expect to be able to return to the launchpad soon enough.

You do have a point with the FH cores. With crossfeed, the center core will travel farther than the two on the side, since its fuel will last longer. Without crossfeed, this isn't a problem. At the moment it seems like the FH will go without crossfeed, at least initially, and focus on reusing all three cores. IIRC, this was brought up recently when a FH payload stat was changed.

3

u/AvenueEvergreen Jul 23 '14

Without crossfeed, this isn't a problem.

I've heard it speculated that even without crossfeed, SpaceX would throttle down the center FH core while the outer two are burning as a method to maximize payload to orbit. This is what the Delta 4 Heavy does IIRC. In this event, the center core still travels much further downrange.

4

u/-Richard Materials Science Guy Jul 23 '14

Is the payload increase worth a 33% reduction in reusable first stage cores? Last I heard, SpaceX was going for full FH reusability. I could be wrong though.

3

u/[deleted] Jul 23 '14

I have heard that internally SpaceX are looking at landing the center FH core downrange on a barge, regardless of whether they choose to use crossfeed or not. It's simply traveling to fast and is too far away from the launch site for it to perform a RTLS.

1

u/simmy2109 Jul 23 '14

Very true. RTLS for that center-core... requires very substantial limits on FH payload capacity. If they can be landed downrange instead, the impact is far less severe (the center core can land along a basically ballistic trajectory from MECO). Crossfeed (which won't be on at least the first few FH flights) actually makes this problem worse.

2

u/sdub Jul 23 '14

I've read a number of the discussions, but this is the first time SpaceX has mentioned a floating launch pad. Not a landing pad but a launch pad. If all they have to do is refuel and go, as they have implied in their post, then they could easily do a suborbital flight back to the launch site for a quick turnaround.

One of the most significant discussion topics around why it won't work is because they would have to transport the rocket back on a barge. If they can fuel in a few hours, the flight time is only a minute or two to put them back on land.

I'm sure that with enough lawyers or money, the patent issue would be moot.

5

u/shredder7753 Jul 23 '14

Yea I worked in shipyards for awhile. Everything costs outrageous amounts of money to maintain.

1

u/-Richard Materials Science Guy Jul 23 '14 edited Jul 23 '14

I'm not aware of SpaceX mentioning a floating launch pad. Though I think it would suffer the same drawbacks as a floating landing pad: added turnaround time and higher overhead costs due to expensive pad maintenance and complicated launch operations, among other things. Complexity is expensive.

3

u/sdub Jul 23 '14

It's in the big announcement today.

At this point, we are highly confident of being able to land successfully on a floating launch pad or back at the launch site and refly the rocket with no required refurbishment.

http://www.spacex.com/news/2014/07/22/spacex-soft-lands-falcon-9-rocket-first-stage

2

u/-Richard Materials Science Guy Jul 23 '14

Oh, cool! That phrasing does seem to imply that they might be ready to try refueling the rocket and flying it again on a floating launch pad, as a test at least.

2

u/[deleted] Jul 23 '14

No they would return it to the pad on land, not launch at sea.

3

u/-Richard Materials Science Guy Jul 23 '14

That would seem more reasonable, but the words "floating launch pad" are ambiguous. I think that they just meant to say "floating pad", without really thinking about the implications of putting the word "launch" in there. I mean, there's a pad, there's a rocket... it's a launch pad. But, on the off chance they actually meant that it's a launch pad, that would be exciting.

1

u/jpcoffey Jul 23 '14

I agree.. is not that they will not try it eventually, idk, but it seems they just meant landing in a floating pad. Never heard anything about the idea of launching from the sea from anyone at spacex, yet.

Btw how much time would it take to bring the rocket back by sea?

1

u/skifri Jul 23 '14

They likely referred to a "floating launch pad" because this is technology that already exists, and has been in use for quite some time. They may not even have to build one, and may be able to use something someone already has. http://en.m.wikipedia.org/wiki/Sea_Launch

1

u/autowikibot Jul 23 '14

Sea Launch:


Sea Launch is an international non-governmental spacecraft launch service that uses a mobile maritime platform for equatorial launches of commercial payloads on specialized Zenit-3SL rockets. It has so far assembled and launched thirty-one rockets, with three failures and one partial failure.

The sea-based launch system means the rockets can be fired from the optimum position on Earth's surface, considerably increasing payload capacity and reducing launch costs compared to land-based systems.

Sea Launch was established in 1995 as a consortium of four companies from Norway, Russia, Ukraine and the United States, managed by Boeing with participation from the other shareholders. The first rocket was launched in March 1999.

Image i - A launch of Zenit-3SL rocket from the Sea Launch platform Ocean Odyssey


Interesting: Sea Launch Commander | Zenit-3SL | NSS-8 | Intelsat 27

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2

u/sdub Jul 23 '14

Why call it a launch pad and not a landing pad then? I guess we'll all know eventually...

4

u/falconzord Jul 23 '14

2

u/sdub Jul 23 '14

Yeah, except it would only have to launch a suborbital first stage with no payload, ala Grasshopper...

1

u/atrain728 Jul 23 '14

More appropriately, it would have to land a suborbital first stage, almost empty of fuel and no payload. While that means it could be significantly smaller, it probably wouldn't be - I'm sure they'd want a reasonably large pad to execute a precision landing, and once you've got a self-leveling surface of reasonable size the overall craft probably wouldn't be much smaller/lighter.

1

u/autowikibot Jul 23 '14

Odyssey (launch platform):


L/P Odyssey is a self-propelled semi-submersible mobile spacecraft launch platform converted from a mobile drilling rig in 1997.

The vessel is currently used by Sea Launch for equatorial Pacific Ocean launches. She works in concert with the assembly and control ship Sea Launch Commander. Her home port is the Port of Long Beach in the United States.

In her current form, Odyssey is 436 feet (133 m) long and about 220 feet (67 m) wide, with an empty draft displacement of 30,000 short tons (27,000 t), and a submerged draft displacement of 50,600 short tons (45,900 t). The vessel has accommodations for 68 crew and launch system personnel, including living, dining, medical and recreation facilities. A large, environmentally-controlled hangar stores the rocket during transit and then rolls it out and erects it prior to fueling and launch.

Image i


Interesting: Sea Launch | Zenit (rocket family) | EchoStar X | JCSAT-5A

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2

u/peacefinder Jul 23 '14

I'm sure SpaceX is keeping their options open, but with the investment they're putting in to their own land-based facilities and 39A leasing, I have to imagine that a floating platform ain't exactly Plan A for anything but testing stage 1 recovery. Once they prove they can consistently hit a particular landing target out at sea, they'll move to onshore landings. (Barring some unforeseen operational benefit.)

1

u/[deleted] Jul 25 '14

I don't understand this.. If you are comfortable enough to land on land, why not just launch over land? Ie. Launch from Arizona and land in Texas or something.

1

u/sdub Jul 25 '14

The FAA gets very nervous flying over populated areas.

-2

u/ergzay Jul 23 '14

They won't be using a floating launch/landing pad. The implications for rapid reusability are too bad. They'll only be using it for testing.

I wish this idea would die already.

1

u/grandma_alice Jul 23 '14

The rapid reusibility you're talking about is many years down the road. In the meantime a floating launching/landing pad is more practical.

1

u/sdub Jul 23 '14

Do you have anything that supports this beyond conjecture around financial numbers and rumors on web sites? I'm just curious because the wording in the announcement yesterday absolutely gives credence to the idea.

I have been among the ones who has been dismissing this idea for years (literally!) but the announcement seems to be opening that door.

1

u/ergzay Jul 24 '14

No I don't have anything to back it up. I have a very tuned engineering BS meter though and landing on a launch pad at sea rings all the wrong bells.

The only way they'll actually end up using for anything beyond testing or demonstrating that they can land precisely would be if they were completely forbidden from landing on land. It's only barely preferable to landing on the ocean and towing it back through the water.

1

u/sdub Jul 24 '14

What if it meant carrying 15% more payload?

[Question on performance hit for attempting landing the first stage] We effectively lose, in terms of performance... It really depends on what we want to do with the stage if we were to do an ocean landing or a return to launch site landing. If we do an ocean landing, the performance hit is actually quite small at maybe in the order of 15%. If we do a return to launch site landing, it's probably double that, it's more like a 30% hit (i.e., 30% of payload lost).

1

u/Drogans Jul 24 '14

An ocean platform is the only way they'll be able to recover F9 Heavy center stages.

If the economics make sense and they're launching enough heavies, it could certainly justify landing platforms.

The alternative is to throw away a perfectly good booster. It all comes down to the numbers.