Booster config and fullfilling delta v

[TeeGee]

Kerbal revelation I had today watching a saturn 5 documentary.

I was watching them assemble the S1 booster for the saturn 5 rocket and saw the cluster engine config used to get the payload up into space when I thought to myself... why don't they use less central engines and fuel but use bigger boosters?

I started staring at the shuttle and realized something... those SRB's donate extra REUSABLE delta v to the rocket. What do I mean? Well, the srbs donate change in velocity for the spacecraft as a whole, are jettisoned, and reused after.

When we built the saturn 5 rocket, every stage was discarded after staging and was not recoverable. So I had a revelation that I needed to test out in KSP, what if I lowered the total fuel and engine count in my central rockets, but used bigger BOOSTERS that I jettisoned and recovered?

SO I went into my VAB to load up my 3 kerbal rocket that had a 4 engine cluster and 4500 delta v (with FAR you really only need 3500 but Im over zealous).

Step 1) I removed all but 1 rocket on the central vehicle and shaved the tank size (I use procedural dynamics) down to about 2300 delta v ish with a TWR or 0.5ish (at launch)

Step 2) I put 2 boosters on the sides, with liquid fuel in each. These boosters DON'T feed off the central tank at all, and once they are empty, are jettisoned ala Shuttle srb style, deploy chutes, and are recovered.

Step 3) I opened KES/Mechjeb and adjusted fuel to satisfy my delta v requirements and launched...

It worked.

Not only did I make it to orbit with MORE than enough fuel, I cut out 1 rocket engine, reused 2 rockets with 2 fuel tanks, and only lost 1 engine + a smaller LF tank in the process.

Before I adjusted to this tactic, I had lost 4 engines and 1 large LF tank in the process of getting 3 kerbals into orbit.

So then I asked myself the question... why doesn't NASA adopt HUGE boosters and smaller core rockets? For example the orion rocket. I think it has 4 or 5 SSME's at the core with 2 SRB's on the sides as boosters.

Why not dump the SRB's and 2-3 of the SSMEs, cut the fuel down in the central vehicle and use stronger LF boosters on the sides that are recoverable? Why not build 2 maybe 3 engine LF boosters if you need it, you can build as large a booster as you want because all of that is coming home after staging?

If I built the Orion rocket, I'd prob use 2 ssmes on the central vehicle, and use the 2x2 engine SSME's as booster rockets. Take the a good chunk of LF/tank space out of the central tank and give it to the staged boosters.

You don't loose lifting ability and you gain more reusability.

[cpast]

There isn't actually any reusability advantage to side staging (provided you allow the stages to separate a bit before firing the upper stage engines, to keep lower stages being damaged by exhaust). It's perfectly possible to recover a first stage that was on a stack; this was in fact planned for the Ares I first stage (which was a solid-fuel rocket, basically a shuttle SRB with an extra segment added). I think the reason it isn't done so much on stacks is that above a certain weight, you cannot effectively recover something with parachutes. The shuttle SRBs used among the largest parachutes ever made; the record was broken by parachutes being tested for the Ares I first stage. Three of these are put on the booster, and they only slow it to 23 m/s at splashdown (admittedly, even empty SRBs weigh 91 metric tons, but still). Taking that kind of impact is not easy, and the shuttle SRBs were among the first heavy rockets built to take it. With liquid rockets, you tend to have more moving parts (such as turbopumps), and you really, really, really don't want to expose it to seawater, and a land touchdown *will* destroy it at those kinds of speeds.

The advantage of side staging has nothing to do with reusability - it's because side-staged engines are never deadweight. That makes side staging beat serial staging, but it might not beat not staging at all (in which case there just aren't deadweight engines, period). It's been used like this for a while - the R-7 and the Atlas missile both use side staging for that reason. However, that mostly affects TWR, which is irrelevant at altitude - hence why side staging is used for the first stage, but not for upper stages.

[Armchair Rocket Scientist]

When we built the saturn 5 rocket, every stage was discarded after staging and was not recoverable. So I had a revelation that I needed to test out in KSP, what if I lowered the total fuel and engine count in my central rockets, but used bigger BOOSTERS that I jettisoned and recovered?

Reusability isn't associated with strapon boosters: every operational rocket I know of besides the Space Shuttle just lets spent SRBs crash into the ocean (this includes the SLS).

SO I went into my VAB to load up my 3 kerbal rocket that had a 4 engine cluster and 4500 delta v (with FAR you really only need 3500 but Im over zealous).

Step 1) I removed all but 1 rocket on the central vehicle and shaved the tank size (I use procedural dynamics) down to about 2300 delta v ish with a TWR or 0.5ish (at launch)

Step 2) I put 2 boosters on the sides, with liquid fuel in each. These boosters DON'T feed off the central tank at all, and once they are empty, are jettisoned ala Shuttle srb style, deploy chutes, and are recovered.

Step 3) I opened KES/Mechjeb and adjusted fuel to satisfy my delta v requirements and launched...

It worked.

Not only did I make it to orbit with MORE than enough fuel, I cut out 1 rocket engine, reused 2 rockets with 2 fuel tanks, and only lost 1 engine + a smaller LF tank in the process.

Before I adjusted to this tactic, I had lost 4 engines and 1 large LF tank in the process of getting 3 kerbals into orbit.

So, basically, you discovered staging?

So then I asked myself the question... why doesn't NASA adopt HUGE boosters and smaller core rockets? For example the orion rocket. I think it has 4 or 5 SSME's at the core with 2 SRB's on the sides as boosters.

The SLS/shuttle already does adopt "huge boosters smaller core," as do most rockets that use SRBs. For example, the Shuttle SRBs have more than twice the thrust of the entire main engine cluster... each. The Ariane 5's SRBs each have nearly 5 times the thrust of the main engine. The boosters may look small, but on the Ariane 5 each booster is heavier than the core, second stage, fairing, and payload. The only reason the boosters look small is that the cores of all the rockets mentioned use hydrogen fuel, which is much less dense than the solid propellants used.

Why not dump the SRB's and 2-3 of the SSMEs, cut the fuel down in the central vehicle and use stronger LF boosters on the sides that are recoverable? Why not build 2 maybe 3 engine LF boosters if you need it, you can build as large a booster as you want because all of that is coming home after staging?

If I built the Orion rocket, I'd prob use 2 ssmes on the central vehicle, and use the 2x2 engine SSME's as booster rockets. Take the a good chunk of LF/tank space out of the central tank and give it to the staged boosters.

You don't loose lifting ability and you gain more reusability.

There are several major problems with this approach.

1: The rocket you proposed would have more than twice the cross-sectional area of the SLS, which is not good for aerodynamics. It's the same reason we don't see "pancake" rockets in real life. It would be more efficient to put all 8 of the booster engines on a giant central core, then replace the central pair with some sort of vacuum-optimized upper stage... which is basically what SLS does.

2: Hydrogen-fueled engines have poor thrust-to-weight ratios, and both the engines and the stages in general have poor thrust-to-cost ratios. The latter is especially true of the SSME. Only one rocket (the Delta IV) launches off of hydrogen alone; most rockets with hydrogen-fueled core stages have powerful SRBs so that lighter and cheaper main engines can be used.

3: Reusability in real life is a lot more complicated than just slapping a parachute on. First of all, the space shuttle SRBs are built like tanks compared to any liquid-fueled booster. At the descent speeds achievable with a parachutes, an LFB's fuel tanks would crumple like a soda can, to say nothing of delicate parts like engine nozzles. For that matter, LFBs would be more susceptible to being torn apart by aerodynamic forces in an uncontrolled descent. Second, the SRBs don't have too many moving parts, so dunking them in seawater isn't that bad, but liquid-fueled engines would require a LOT of refurbishment after a splashdown. Third, the more dV the boosters contribute, the faster they'll be going at separation. Too fast, and they'll burn up or be torn apart on reentry.

So, let's say we want to redesign the SLS with giant reusable liquid-fueled boosters. First of all, we don't want hydrogen providing most of the takeoff thrust, so we'll switch to kerosene. While we're at it, let's make the core stage kerosene too so we don't have to deal with different refueling equipment. The boosters can't handle a splashdown, so they'll have to perform a powered landing either back at the launch site or downrange on a floating platform. This means many engines on the booster so that it can provide very low thrust when it needs to. They also can't contribute too much dV or we'd waste a lot of fuel slowing down enough to survive reentry. About the size of the core stage is a good maximum. But if our boosters are about the size of the core stage, we might as well make them identical and use a lot of the same hardware. Since they're using the same fuel, we can boost the payload capacity by adding fuel crossfeed.

Ya know, this rocket is starting to look kinda familiar...

[sgt_flyer]

Liquid fuel boosters for the SLS is already something being researched on, for future SLS upgrades.

Among the contestants for advanced boosters design for SLS block II, P&W, Rocketdyne and dynetics have associated to revive Saturn V F-1 engine, to create the Pyrios booster - a Kerolox booster, each booster propelled by two of their F-1B engines, - the ISP advantage the pyrios would have over other planned Block II SRB would allow SLS to lift 20 more tons than it's competitors.

KSP LFB KR1x2 is modelled after the pyrios booster concept art.

(Besides, one of the other advantages of LFB would be to lower drastically the weight the Crawler would have to transport to the pad - they would be fueled only one in position, whereas the SRB's are full before getting out of the VAB.) - for an idea,in prevision for the various SLS configurations they had to increase the crawler's lifting weight from 5400 metric tons to 8200 metric tons.

[R0cketC0der]

Aside from the problems others have mentioned, reusability doesn't directly translate to a lower launch price. The SLS can lift (on paper) 70 tons with not a single reusable part while costing about the same price per launch as the shuttle, which was only able to lift 25 tones per launch and being mostly reusable.

Analysis has shown that reusing the boosters from the shuttle did not have any costs benefits, which is also the reasons why the SRBs on the SLS aren't going to be reused. Also, reusing the orbiter was highly ineffective, because a big amount of maintenance had to be done between the launches.

[TeeGee]

Reusability isn't associated with strapon boosters: every operational rocket I know of besides the Space Shuttle just lets spent SRBs crash into the ocean (this includes the SLS).

So, basically, you discovered staging?

The SLS/shuttle already does adopt "huge boosters smaller core," as do most rockets that use SRBs. For example, the Shuttle SRBs have more than twice the thrust of the entire main engine cluster... each. The Ariane 5's SRBs each have nearly 5 times the thrust of the main engine. The boosters may look small, but on the Ariane 5 each booster is heavier than the core, second stage, fairing, and payload. The only reason the boosters look small is that the cores of all the rockets mentioned use hydrogen fuel, which is much less dense than the solid propellants used.

There are several major problems with this approach.

1: The rocket you proposed would have more than twice the cross-sectional area of the SLS, which is not good for aerodynamics. It's the same reason we don't see "pancake" rockets in real life. It would be more efficient to put all 8 of the booster engines on a giant central core, then replace the central pair with some sort of vacuum-optimized upper stage... which is basically what SLS does.

2: Hydrogen-fueled engines have poor thrust-to-weight ratios, and both the engines and the stages in general have poor thrust-to-cost ratios. The latter is especially true of the SSME. Only one rocket (the Delta IV) launches off of hydrogen alone; most rockets with hydrogen-fueled core stages have powerful SRBs so that lighter and cheaper main engines can be used.

3: Reusability in real life is a lot more complicated than just slapping a parachute on. First of all, the space shuttle SRBs are built like tanks compared to any liquid-fueled booster. At the descent speeds achievable with a parachutes, an LFB's fuel tanks would crumple like a soda can, to say nothing of delicate parts like engine nozzles. For that matter, LFBs would be more susceptible to being torn apart by aerodynamic forces in an uncontrolled descent. Second, the SRBs don't have too many moving parts, so dunking them in seawater isn't that bad, but liquid-fueled engines would require a LOT of refurbishment after a splashdown. Third, the more dV the boosters contribute, the faster they'll be going at separation. Too fast, and they'll burn up or be torn apart on reentry.

So, let's say we want to redesign the SLS with giant reusable liquid-fueled boosters. First of all, we don't want hydrogen providing most of the takeoff thrust, so we'll switch to kerosene. While we're at it, let's make the core stage kerosene too so we don't have to deal with different refueling equipment. The boosters can't handle a splashdown, so they'll have to perform a powered landing either back at the launch site or downrange on a floating platform. This means many engines on the booster so that it can provide very low thrust when it needs to. They also can't contribute too much dV or we'd waste a lot of fuel slowing down enough to survive reentry. About the size of the core stage is a good maximum. But if our boosters are about the size of the core stage, we might as well make them identical and use a lot of the same hardware. Since they're using the same fuel, we can boost the payload capacity by adding fuel crossfeed.

Ya know, this rocket is starting to look kinda familiar...

What I was trying to say was building a craft that had almost half of its delta v come from its boosters and the rest off of its core rocket.

I would never use hydrolox as a fuel for a lifting rocket. It's way too volume inefficient and requires massive tanks to provide sufficient delta v to make orbit.

Instead of building a rocket that is "pancaked", why not build a taller, thin rocket with a lower aerodynamic cross section?

The only real issue is that LF boosters are delicate and don't take splashdown or sea water very well. Or if you give it too much delta v, they may burn up on reentry. I personally think it is worth investing research on finding ways to give boosters more delta v and better survivability for reuse.

Why can't LF boosters use convection cooling from the tanks to protect it from reentry heat? For example, like the SSME's do. During staging, keep some liquid fuel/oxidizer circulating around the tank like ribs that would help cool the rocket as it reenters the atmosphere.

Build lighter parachutes OR keep the cooled fuel you used as reentry protection to slow down the rocket moments before splashdown.

[Nibb31]

I was watching them assemble the S1 booster for the saturn 5 rocket and saw the cluster engine config used to get the payload up into space when I thought to myself... why don't they use less central engines and fuel but use bigger boosters?

In the 60s, NASA had an aversion for using SRBs on manned vehicles for safety reasons. SRBs cannot be shut down, and so they were seen as a hazard.

This went out of the window with the Shuttle, because it was either SRBs or no Shuttle.

I started staring at the shuttle and realized something... those SRB's donate extra REUSABLE delta v to the rocket. What do I mean? Well, the srbs donate change in velocity for the spacecraft as a whole, are jettisoned, and reused after.

SRBs aren't reusable. The expensive bit of an SRB is molding the solid fuel inside the booster, but that's gone once you've burnt it up. The only thing you get back are the casings, which are basically dumb steel tubes. They reused those casings for political reasons, but there was no cost advantage in doing so. Steel tubes are cheap.

So then I asked myself the question... why doesn't NASA adopt HUGE boosters and smaller core rockets? For example the orion rocket. I think it has 4 or 5 SSME's at the core with 2 SRB's on the sides as boosters.

There is no Orion rocket. It's called SLS.

Why not dump the SRB's and 2-3 of the SSMEs, cut the fuel down in the central vehicle and use stronger LF boosters on the sides that are recoverable? Why not build 2 maybe 3 engine LF boosters if you need it, you can build as large a booster as you want because all of that is coming home after staging?

The difficulty is in recovering liquid engines. If you dunk them in sea water, they are dead. If they land with wings, hydraulics, and landing gear, then they require too much extra weight. If they land with parachutes on the ground, they will dent, ding, flex, break, or whatever.

Since launches are always over water, to bring them back to land requires an RTLS manoeuver, which costs extra fuel, and therefore payload penalty.

Only until recently has SpaceX been exploring propulsive landing, but that also has a payload penalty.

In the end, it's a very difficult engineering problem and the cost of adding reusability simply isn't worth it economically. Reusability only makes sense if there is enough demand to make it worthwhile. Currently, there isn't, so it is more efficient to make rocket engines as cheap as possible so that expending them doesn't carry as much of a penalty.

Edited June 21, 2014 by Nibb31

[TeeGee]

In the 60s, NASA had an aversion for using SRBs on manned vehicles for safety reasons. SRBs cannot be shut down, and so they were seen as a hazard.

This went out of the window with the Shuttle, because it was either SRBs or no Shuttle.

SRBs aren't reusable. The expensive bit of an SRB is molding the solid fuel inside the booster, but that's gone once you've burnt it up. The only thing you get back are the casings, which are basically dumb steel tubes. They reused those casings for political reasons, but there was no cost advantage in doing so. Steel tubes are cheap.

There is no Orion rocket. It's called SLS.

The difficulty is in recovering liquid engines. If you dunk them in sea water, they are dead. If they land with wings, hydraulics, and landing gear, then they require too much extra weight. If they land with parachutes on the ground, they will dent, ding, flex, break, or whatever.

Since launches are always over water, to bring them back to land requires an RTLS manoeuver, which costs extra fuel, and therefore payload penalty.

Only until recently has SpaceX been exploring propulsive landing, but that also has a payload penalty.

In the end, it's a very difficult engineering problem and the cost of adding reusability simply isn't worth it economically. Reusability only makes sense if there is enough demand to make it worthwhile. Currently, there isn't, so it is more efficient to make rocket engines as cheap as possible so that expending them doesn't carry as much of a penalty.

Awesome! Thanks for the answer!

[Armchair Rocket Scientist]

What I was trying to say was building a craft that had almost half of its delta v come from its boosters and the rest off of its core rocket.

Half the dV on the first stage is about what the Falcon 9 first stage gets, so reentry should be fine with a fairly small braking burn.

However, even with a metholox stage with a mass ratio of almost 25, the boosters would have to be 80% of the rocket's liftoff mass (by comparison, if the boosters are the same size as the core, they'd be less than 67% of the liftoff mass). Also, since the core stage would be burning at the same time as the boosters, they'd actually be going a bit faster at burnout.

The only real issue is that LF boosters are delicate and don't take splashdown or sea water very well. Or if you give it too much delta v, they may burn up on reentry. I personally think it is worth investing research on finding ways to give boosters more delta v and better survivability for reuse.

Why can't LF boosters use convection cooling from the tanks to protect it from reentry heat? For example, like the SSME's do. During staging, keep some liquid fuel/oxidizer circulating around the tank like ribs that would help cool the rocket as it reenters the atmosphere.

First off, you'd have to run literally thousands of little pipes around the entire outside of the stage. This plumbing is going to be heavy and very expensive to manufacture.

Running oxygen or methane through the pipes is a very bad idea: even at room temperature you can't liquify them with any amount of pressure. That means you'd have to boil off the fuel to cool the vehicle, essentially using it like an ablative heat shield. Since oxygen and methane can't absorb that much heat by boiling, this fuel would be put to much better use with a braking burn, with the added advantage of not requiring the heavy plumbing. For that matter, an actual ablative heat shield - most likely using some kind of spray-on coating would be more effective.

Active cooling systems have been proposed for spacecraft, but generally for things like SSTO spaceplanes on the way up (which would have significant aerodynamic heating with the engines running, meaning you could immediately burn the boiled fuel), or orbital reentry (where the speeds are so high that braking burns aren't practical).

Build lighter parachutes OR keep the cooled fuel you used as reentry protection to slow down the rocket moments before splashdown.

Propulsive splashdown partially solves the structural issues, although the stage could still topple over after its engines were underwater and smack its upper section into the surface (I've lost some stages like this in KSP), and liquid engines still don't like saltwater.

One idea I really like for lower-stage reusability is the BDB (Big Dumb Boat) approach. Basically, you land the stage on a floating platform downrange of the launch site. Semi-submersible vessels are very popular for deep water oil drilling because they're very stable even with wave action, which also happens to be a desirable trait when you're trying to land a tall rocket stage on one. Used oil platforms are about a hundred million dollars, and new ones a few times more, so $200M for a landing platform is reasonable.

The platform would be towed into position approximately where the first stage would land by tugboats. At launch time, the tugboats and all personnel would station themselves several miles away, and the stage would guide itself to a propulsive landing. Once the stage is safely landed, the crew would return and perform any necessary post-flight checks. At this point, the stage could either be partially refueled and fitted with an aerodynamic nose cap, then fly itself back to the launch site (giving turnaround times of a few hours) or be loaded onto a boat and sailed back to the launch site (still allowing turnaround of less than 24 hours).

Now, SpaceX wants "single digit hours" turnaround with their lower stages. However, this wouldn't allow much more than a preliminary "are there gaping holes in the airframe or missing engines) inspection before slapping on a second stage and payload, refueling, and launching again. Besides, a launch provider doing 200 flights a year (a lot) with a fleet of 5 reusable vehicles would only need to launch an individual vehicle every 9 days. Also, on a fully reusable vehicle the second stage wouldn't even be back yet.

In theory, a second landing platform could be used, with one for low-inclination orbits and one for high-inclination orbits, meaning less time and fuel spent towing multi-kiloton platforms around.

Now, this approach would be great for the core stage of a rocket with big boosters (such as the Falcon Heavy core), which would be going too fast to return to the launch site. However, the boosters would probably be going slowly enough to just boost back to the launch site.

[xcorps]

Semi-submersible vessels are very popular for deep water oil drilling because they're very stable even with wave action, which also happens to be a desirable trait when you're trying to land a tall rocket stage on one. Used oil platforms are about a hundred million dollars, and new ones a few times more, so $200M for a landing platform is reasonable.

I'd like to see the engineering that could land a spent booster on a semi. I work in offshore drilling in logistical support. I travel to semi submersible rigs, drill ships, production platforms etc daily.

You'd have to restructure the rig, removing the derrick and building the quarters BELOW the rig floor, which adds about 25 million. Then you'd have to pick the perfect spot in the ocean to tow it too, which is upwards of $10,000 an hour. Then you have to plot the descent of a spent engine so perfectly without regard to wind changes or other factors to get it to land on the rig...no way.

Oh, and you'd have to use a rig with dynamic positioning and not anchors, because of water depth. That's means a MODU, which means it's going to be more than 150 million for a semi submersible.

Forget that. No way.

Edited June 23, 2014 by xcorps

[Nibb31]

I'd like to see the engineering that could land a spent booster on a semi. I work in offshore drilling in logistical support. I travel to semi submersible rigs, drill ships, production platforms etc daily.

You'd have to restructure the rig, removing the derrick and building the quarters BELOW the rig floor, which adds about 25 million. Then you'd have to pick the perfect spot in the ocean to tow it too, which is upwards of $10,000 an hour.

It's a one-time expense, and a first stage costs several million dollars, so you might make up for it in the long. It's also not much more expensive than building a whole new conventional launch pad, and SpaceX are planning at least 3 of those.

You won't need crew quarters at all. Any crew would live on a service ship that would only dock to the rig when necessary. Operations would be much simpler than what Sea Launch does.

Then you have to plot the descent of a spent engine so perfectly without regard to wind changes or other factors to get it to land on the rig...no way.

SpaceX is aiming for pinpoint landing capability. Using a off shore platform wouldn't be much different to landing on a 10x10-meter concrete landing pad. However, it would avoid wasting propellant on the flipback RTLS manoeuver and allow a more optimal trajectory, which would drastically increase payload capacity.

Oh, and you'd have to use a rig with dynamic positioning and not anchors, because of water depth. That's means a MODU, which means it's going to be more than 150 million for a semi submersible.

Forget that. No way.

I don't think the Gulf of Mexico is that deep, and there are already plenty of oil-rigs out there. It would be ideal to land rockets there from a Texas launch site.

I'm not familiar with much of the technicalities of off-shore platforms, but Sea Launch already uses one for launches, and Italy also has a (somewhat smaller) launch platform off the coast of Kenya, so it's not that far fetched.

Edited June 23, 2014 by Nibb31

[Armchair Rocket Scientist]

It's a one-time expense, and a first stage costs several million dollars, so you might make up for it in the long. It's also not much more expensive than building a whole new conventional launch pad, and SpaceX are planning at least 3 of those.

Well, ships still require maintenance, fuel, etc. That being said, a landing platform wouldn't have a lot of the fancy on-deck equipment an operating oil platform has. The most important equipment would be some type of crane to secure the rocket after landing and possibly load it onto a transport ship; there are already semisubmersible Crane Vessels, but they're designed to lift thousands of tons, and probably that useful something delicate like a rocket.

There would also probably need to be systems to handle leftover fuel; LOX could just be vented, as could nitrogen or helium from cold gas systems, and methane would be best off burned (it isn't particularly toxic, but it's a much stronger greenhouse gas than its combustion products). Kerosene and other liquid hydrocarbons would need to be captured and stored, as would any hypergolic propellants.

SpaceX is aiming for pinpoint landing capability. Using a off shore platform wouldn't be much different to landing on a 10x10-meter concrete landing pad. However, it would avoid wasting propellant on the flipback RTLS manoeuver and allow a more optimal trajectory, which would drastically increase payload capacity.

Pretty much. I believe SpaceX has said a downrange propulsive landing (which they're only doing for tests) means a 15% payload hit, vs. 30% for boostback. Essentially, you're sacrificing a fixed investment equivalent to building several new 1st stage cores, and maybe 1 core worth of maintenance per year, for a 20% payload increase. With the Falcon Heavy core though, boostback would be pretty much impossible, and there's not much the right distance downrange from Texas. For that matter, polar orbits don't offer many convenient islands. Launching north from Puerto Rico it might be possible to reach the US East Coast with some fancy manuevering, but it would take a lot of dV.

I don't think the Gulf of Mexico is that deep, and there are already plenty of oil-rigs out there. It would be ideal to land rockets there from a Texas launch site.

The Gulf of Mexico is that deep, at least in the parts where it's convenient to land a rocket. Most of the oil wells are in relatively shallow water on the continental shelf and slope, but from SpaceX's Texas site, the best landing sites would be 2-3 km deep. Besides which, IIRC Elon Musk has said that the FH core would overshoot Florida from Texas, which means the landing area would be over 5 km deep. The same would be true for any launches from Florida, and any polar launches from California or Puerto Rico.

[xcorps]

http://i566.photobucket.com/albums/ss102/OMBugge/Offshore%20Pics/technip_spars.png

That's a drawing of some of the water depths that are currently being drilled, just FYI. Those are production platforms, permanent installations placed after the well is drilled to control flow. The actual drilling is done by either Dynamic Positioning semisubmersibles or drilling ships.

As for a pinpoint landing of 10mx10m offshore, let's just say I'm highly skeptical. You'd be better off with an inflatable raft system mounted to the booster and then having something like this

pick it up. The crane on that boat is rated to pick up 87.5 long tons from a sea floor of 10,000 ft. At sea level I think it's 100 long tons.

from SpaceX's Texas site, the best landing sites would be 2-3 km deep. Besides which, IIRC Elon Musk has said that the FH core would overshoot Florida from Texas, which means the landing area would be over 5 km deep. The same would be true for any launches from Florida, and any polar launches from California or Puerto Rico.

Once you pass about 1000ft, the depth doesn't matter anymore. I think there's a couple of semi submersibles that still rely on anchors out to 1500ft, but it's too expensive to run anchors (there's up to 12 per leg, requiring up to 4 tugs to handle them) when you can just use dynamic positioning.

Edited June 23, 2014 by xcorps

[R0cketC0der]

http://i566.photobucket.com/albums/ss102/OMBugge/Offshore%20Pics/technip_spars.png

That's a drawing of some of the water depths that are currently being drilled, just FYI.

As for a pinpoint landing of 10mx10m offshore, let's just say I'm highly skeptical. You'd be better off with an inflatable raft system mounted to the booster and then having something like this http://www.maritime-executive.com/media/filter/large/img/HGIM_Harvey_Deep-Sea.jpg

pick it up. The crane on that boat is rated to pick up 47.5 long tons from a sea floor of 10,000 ft.

As already mentioned often in this thread, liquid engines don't like sea water.

Also, the grasshopper and F9R tests that have been done prove that it can land with a very high accuracy. They still need to be able to control the descent path further, but the final touchdown can be done with pinpoint accuracy. And for the control of the descent path, the grid fins in the latest F9R test look pretty promising. I would definitely bet that it will be able to land with pinpoint accuracy.

Also, the RTLS maneuver seems a lot better than landing at some point offshore to me. Of course you loose a little bit more payload capacity, but you save money for the building and maintenance of an offshore platforms and ships and you can do all the maintenance and testing of the landed stage almost immediately.

[xcorps]

As already mentioned often in this thread, liquid engines don't like sea water.

Also, the grasshopper and F9R tests that have been done prove that it can land with a very high accuracy. They still need to be able to control the descent path further, but the final touchdown can be done with pinpoint accuracy. And for the control of the descent path, the grid fins in the latest F9R test look pretty promising. I would definitely bet that it will be able to land with pinpoint accuracy.

As I said, pinpoint offshore. I know it's been done on land.

What's the touchdown speed?

What's the max wind speed that the spent booster can be controlled after the chutes have deployed?

[R0cketC0der]

As I said, pinpoint offshore. I know it's been done on land.

What's the touchdown speed?

What's the max wind speed that the spent booster can be controlled after the chutes have deployed?

SpaceX doesn't use chutes, they go full powered landing instead. My guess would be that the touchdown speed is somewhere in the range of 1 to 5m/s, though I don't know exact numbers. Wind won't be much of a problem during the final landing burn because that only lasts a few seconds, but it will probably affect the booster a lot during unpowered descent.

[xcorps]

Ah, this whole conversation I was thinking it was dead boosters. I'll shut up now.