How NASA Reused Rocket Boosters Before SpaceX Transcript, AI Summary & Key Points

00:04 Hello, it's Scott Manley here. Many of you have probably seen the recent footage of Starship 40 being towed back home after 3 weeks of floating around in the ocean. Now granted, it's not in great condition. Partly because of the conditions at sea and partly because the recovery crews were trying to figure out how to tow this thing and damage it along the way.

00:22 But for three decades, NASA was towing large pieces of space hardware back to land after they landed in the ocean after every single space shuttle launch. They went out into the Atlantic and they found a pair of 100 ton solid rocket boosters and brought them home so they could fly again. The majority of the launch thrust for the space shuttle came from those two massive solid rocket motors.

00:46 each developed about 1,500 tons of thrust and together they massed about 1,200 tons and that's over half the mass of the space shuttle at liftoff. Now 2 minutes after liftoff they've burned through most of their propellant and they they burn out and they are separated from the external tank and at that point they're moving at something like 3,000 mph or 4,800 km/h.

01:07 They're like 47 km up. They're trailing smoke then sparks as there's a small amount of leftover propellent that continues to burn. Now the shuttle continues on to award the orbit. But these boosters they continue on a parabolic arc eventually reaching an altitude of about 70 km or 230,000 ft and then they start falling back into the atmosphere in a steep re-entry.

01:34 During this entry, dynamic pressure peaks at something like 100 atmospheres. There's no attitude control in these. are just big steel tubes that tumble, but the atmosphere slows them down to subsonic speeds by the time they are ready to deploy their parachutes. And that is around 15,700 ft where the sequence initiates and it's triggered by a pressure sensor.

01:53 At that point, they're probably moving around 370 mph. It's like 600 km/h. So, a nose cap is blown off and a small pilot parachute comes out and that pilot chute then pulls out the drogue parachute. And the drogue is like a 54 foot conicle ribbon parachute. It doesn't just slam open. It opens very carefully to reduce the stress on everything. And eventually it takes about uh it it does it finishes up about 9,000 ft.

02:21 At that point the booster has slowed a little. The drogue isn't really slowing the par the booster down. What it's doing is it's stabilizing the booster so it's vertical. And then a few seconds later, once it's dropped to about 5,500 ft, the top then separates again. The frustr comes off and this gets pulled away from the forward skirt. And that action that extracts the three main parachutes from their deployment bags.

02:48 So the frustr about 60 mph, but those three main parachutes, they begin their own staged opening. They unfurl. They first inflate like 20% and then 40% and eventually they are fully open with about 1,000 ft to spare. Just before it hits the ocean, the uh booster ejects the nozzle extension. This is because the nozzle extension would break on impact and by in doing that it would also generate a lot of forces against the thrust vector control hardware and that could damage that.

03:25 So they sacrificed the nozzle to save the ve the hardware there. The water impact happens at about 50 mph or 80 km an hour. That's about 400 seconds after launch. This is usually about 135 nautical miles downrange, but it could vary depending upon the mission profile. So, both boosters would usually land inside a footprint about 6x 9 miles. They hit nearly vertically and as they do so, the open end of the booster lets in water which rapidly fills the booster.

03:56 You got to remember these are just big steel tubes with thick walls. They mass about 91 tons empty. They then settle into what is called uh the spar mode by the recovery team. They're essentially floating up upright with about the forward 20% sticking out of the water because the air still is still entrapped inside the empty casing. That impact speed, by the way, isn't the original number.

04:21 The first main parachutes were the small main parachutes only 115 ft in diameter and they produced an impact speed closer to 100 km/h. But starting with STS 41D in 1984, they began flying the large main parachutes 136 ft across. Those brought the impact speed down by about 20% and they were fully incorporated into the program by uh STS-51D in 1985. So the two bigger canopies did two useful things, right?

04:51 They would lower the structural loads on booster impact, but they also improved the single parachute failure survivability. If one of the three shoots failed, the remaining two would give the same drag as the original three small ones. And so offshore in the Atlantic waiting for those boosters, there were two ships which look a lot like offshore oil field supply vessels.

05:16 There was the Liberty Star and the Freedom Star. And these were both built in the 1970s specifically for this job. There was actually a third one that was built by the Air Force. It was named Independence because the Air Force were wanting to launch from the West Coast and so they would need ships to recover the boosters there. As it happens, the launch, you know, the West Coast launches never happened.

05:35 And that ship ended up being chartered by the Navy, Noah, and others. But yeah, the ships for this were designed specifically from the Keup for this task. They were like 176 ft long, 37 ft wide, and they had a draft of 12 feet, displacing about 1,000 tons. They were powered by a pair of diesel engines delivering 2900 horsepower that could drive the main propellers, the generators, thrusters, all the supporting equipment.

06:02 Now, one of the more interesting design features for these was the thruster arrangement. Each ship had bow and stern thrusters. These are enclosed water jets so that they can move in any direction without relying on the main propellers. Those thrusters were originally a requirement because the ships h were going to have to transit the Banana River and the Port Canaveral channels, waters that have manatees in them.

06:26 Right now, traditional open propellers and Florida manatees do not mix well. As it turns out, however, those same thrusters made the actual recovery work far safer. When you're trying to hold precise position next to a floating booster with divers in the water and long parachute lines everywhere, the last thing you want is a spinning open propeller that can foul a line or injure someone.

06:50 The ships would leave port the day before the launch, and they would pre-position about 8 to 10 miles from the predicted landing zone. If the skies were clear, the shuttle would be visible above the horizon within a minute of launch, and the crew would be able to see the booster separation, watching them leave smoking trails in the sky and heading towards the predicted landing points.

07:13 Using binoculars, the crew could observe the parachute deployment and the landing. Also, they would hear sonic booms generated by the boosters as they returned. After splashdown, the ships moved in. First, they would recover the first room, the pilot shoot, the drogue, and the three main parachutes. Those would all get wound onto large reels on deck because the parachutes would be inspected, untangled, refurbished, and reused for multiple flights, but the booster was the main part of the operation.

07:43 So, they would uh put in the water a pair of small rigid hull inflatable boards. They would boats, they would have a bunch of specialist crews on board with specialist recovery gear. First thing they would do is a visual inspection on the surface and then the dive crew would get in the water and they'd inspect the booster. And when they were ready, they would bring out something called the diver operated plug or DOP.

08:05 This was designed to be a neutally buoyant device that could be moved around underwater by the divers. They would have to descend about 110 ft to the nozzle at the bottom of the booster. And then they would insert the DOP into the bottom of the booster, inflate it, and then that would plug up the bottom of the booster. Once that was sealed, they would have an airline that ran to the recovery ship, and that would start pumping in air into the casing, and that would increase the air pressure inside and force the water

08:34 out. So, as this happened, gradually the booster would get lighter. it would rise up and it would transition from like a vertical mode into a sort of semilog mode and then eventually into a log mode where it floated sideways on the surface. And in that attitude, it could then be towed without the risk of it standing back up in a swell and breaking the tow line or the air hose or anything.

08:56 Now, doing all this would take at minimum 4 hours, sometimes 8 hours or more depending upon the conditions. Each ship would recover one booster and once secured it would be taken under tow back towards Port Canaveral. Now depending on the seasate, the returns trip could take the better part of a day. The boosters would be towed through the port and up the banana river to a special dock next to hangar AF.

09:22 Here the boosters were lifted out of the water with large cranes set on transporter dollies and moved inside. They were thoroughly washed to remove the salt water, disassembled into their segments, inspected, and prepared to be shipped back to the manufacturer in Utah for proper refurbishment and reloading with propellant. And these segments are still flying today on SLS.

09:43 Now, those same ships also picked up a second major job starting in 1998. During the downtime between launches, they began towing the Pegasus barge that carried the brand new external tanks from the Mishud assembly facility near near New Orleans all the way to the Kennedy Space Center. The ships received structural upgrades so they could handle the heavier towing loads from this.

10:07 Freedom Star would make the first of these toes in June of 1998, and both vessels continue to do this work through the final tank deliveries of the program. And when the Colombia disaster happened, they also towed the barges in the opposite direction with the previously delivered tanks back to New Orleans so that they could be inspected as part of the Colombia investigation.

10:31 So now the booster recovery system did not arrive fully formed. The first few years were a series of hard lessons that forced changes in the technology, the hardware, the procedures. STS3, one of the main parachutes, became entangled with a flotation device that had been installed to help recover the shoots after they hit the water. Right? Meaning that the booster landed on only two parachutes at 120 km or an hour.

10:56 The booster received significant damage to the aft skirt area. And so, uh, they decided to maybe get rid of these floats and just leave the things attached and separate. uh on landing STS4 in June 1992. Well, they didn't have the flotation devices anymore, but then a serious failure occurred. The system that was supposed to detach the parachute lines upon landing was triggered by GLload.

11:21 And uh the basically when the first drum disconnected, uh the bang was enough to activate those cutters. And so the parachutes were basically disconnected on both boosters at the same time the mains were supposed to deploy. So yeah, both boosters fell into the water without any parachutes attached. They broke up and they were, you know, sank in 3,000 ft of water.

11:46 So, yes, the uh recovery ships in that case unfortunately had to return to port empty-handed, but the recovery boats did then go back out later with some specialized remotely operated submersibles and sonar equipment, and they located the broken boosters on the seafloor so they could capture imagery to understand what went wrong in this case and fix the problem.

12:09 So yeah, with the risk of the parachute attachment, uh they decided to stop detaching the parachutes from STS5 and onwards. So the G switches were basically deactivated and this meant that divers would have to go in and manually detach the parachute lines by hand after every booster landing and this was problematic in itself. So in the vertical orientation, the top of the booster would be high above the water, so you couldn't detach it there.

12:36 The parachutes were designed to be detached using a mechanical link at the top of the risers and those would hang about like onethird of the way down the booster. So that would be underwater maybe 20 30 ft. But in high seas this was still very close to the surface and divers could actually get into trouble getting battered by the waves or getting lifted up by them, getting crushed by them.

12:56 And so after a whole bunch of time, they ultimately replaced the mechanical links with a timer mechanism so that the fittings would release when the boosters were supposed to hit the surface, right? And uh automatic release did great except that it showed up a new problem called slapdown damage. When the boosters hit the water, they could be moving sideways because of the wind.

13:19 And if the wind was fast enough, say about 30 mph, they would feel the drag of the water at the bottom. And without the parachutes at the top applying drag, the top of the booster, it would just like pitch over really fast and the top of the booster could slap into the water hard enough to damage the forward skirt. And there was a lot of concern about damage to this particular area because they didn't actually have many spares.

13:44 And if this was damaged, like it may be impossible to repair it and it might be impossible to find spare parts. So it was reasoned that if the parachutes remained attached during the initial splashdown, it would add enough drag and resistance to the top of the booster and it would counteract the rotation somewhat. So a new parachute design mechanism was developed using a saltwater automatic release mechanism.

14:08 This is a common piece of hardware in parachutes used by the military. For example, in ejection seats, it ensures that the parachutes will separate from the person when they land in the water and not get tangled in their shoots. So NASA just needed to make massively larger versions of these things for the booster parachutes. So starting with STS86 in September 1997, the program switched to seawater activated switches.

14:34 And so that problem was effectively solved. But even then, perfect weather sometimes would make things hard, right? If there was zero wind, the parachutes might settle elegantly over the top of the booster and that those would require like a lot of work to remove them. They would have to like plug up the booster and dewater it until it tipped over enough that a diver could step up on top of the booster, walk to the top, and then spend the next 30 minutes trying to carefully take the parachute off the top.

15:02 The plug also had a few problems. after the nozzle is sealed and you start pumping air in. The water will uh keep getting pushed out, but after the launch, like it's not clean inside of there. You've just been burning fuel and stuff and there's like debris left inside the casing. Things like thermal insulation and that loose material could actually block up the drain port.

15:22 And if the air was being pumped in and the water wasn't getting out, then eventually the DOP would pop out like a cork, like a really massive one- ton cork. it would make a lot of noise and there was concern that the damage uh they could cause damage to the booster or even observers who might have been wondering whether the boo why the booster wasn't draining right so they tried using like wire basket style debris strainers or filters and that didn't solve the problem instead they would develop the enhanced diver

15:55 operated plug which included a burst disc and die packages so if the booster got uh pressure got too high the disc would pop, the water would turn like fluorescent green and it would be obvious that they needed to stop pumping air and maybe like if they get a break in the weather, they would pull the cork out or the pop the plug out and uh try the whole thing again.

16:16 Boosters also uh sometimes got too close. In the case of STS 1116, there's a photo showing two boosters right next to each other. They landed about half a mile apart. one was sitting slightly higher in the water because you know they would trap different amounts of air. So the one sitting higher in the water is feeling more of the wind so it moved faster and by sheer bad luck they came really close to each other and the parachutes were tangled.

16:43 So the support ships, you know, they tried to recover as much of the parachutes as possible and the people back at the the hangar had a lot of work to do detangling these things. And the recovery ships also got pressed into a much darker duty. In January 1986, the day Challenger was lost. Liberty Star and Freedom were supposed to be on station about 130 mi off the coast.

17:07 Ashore, it was a crystal clear, bitterly cold day. Ice had formed on the launch towers because a strong cold front had just passed through offshore. That same cold front was producing one of the worst non-tropical storms of the entire program. The ships spent 2 days out there in sustained 60 mph winds and 15 to 25 ft seas. They couldn't do anything but basically keep their bows pointed into the waves.

17:33 The pounding was hard enough that the paint cracked on the decks. After the storm passed, the ships were a long way from their designation mission support positions. And while they began heading back, they were still about 30 miles away from where they were supposed to be when the ill- fated launch happened. Now, after the accident, their mission immediately changed from booster recovery to debris location and salvage support.

17:57 They spent months helping search for wreckage as part of the larger Navy and contractor effort and they eventually recovered critical pieces of the right-hand solid rocket booster joint and a great deal of other debris. And then there were the uninvited observers in the early 1980s during the Cold War. Soviet intelligence gathering trwers, large ships covered with antennas, they they would routinely shadow the recovery force.

18:23 On at least one early mission, a Soviet trwler would position itself right in the impact zone, and it ran up at the International Code of Signals flags, claiming that it was broken down and unable to maneuver. The Coast Guard cutter that was on station with the recovery ships uh chose to answer with its own flag hoist. They would offer to come over and tow the disabled vessel.

18:46 And as soon as that signal went up, a swirl of water appeared behind the Soviet ship as its propellers engaged and it moved out of the way. The recovery ships finished their work while the twler watched from a few hundred yards off. After several of those little games, the Soviet vessels mostly stopped interfering, though they continue to linger in the area for years longer.

19:05 So, across 135 shuttle missions, 266 of the 270 boosters that flew were successfully recovered and returned for refurbishment. The two lost on STS4 and the pair from Challenger were the primary exceptions. What began as an experimental ocean retrieval concept would become a routine maritime operation that supported every flight of the space shuttle program.

19:31 However, the bean counters did end up figuring out that it didn't really save them that much money. When NASA later designed the five segment boosters for this SLS, they looked at the recovery process again and they ultimately decided against it. the weight of the parachutes, the first drum, the flotation devices, and the associated hardware. It simply wasn't justified, especially considering the much lower flight rate and the extensive heritage data that they already had.

19:58 The SLS boosters, therefore, are being expended. The ships were no longer needed, and those moved on. The Liberty Star was transferred to the US Merchant Marine Academy, and it was renamed to the King's Pointer. The Freedom Star is at the Paul Hill Center for Maritime Training and Education and it retains its original name. And so yes, while everyone is fascinated by SpaceX towing Starship back after 3 weeks, remember that NASA did the same thing successfully for three decades, hundreds of times, and they reflu the

20:34 parts which had splashed down into the saltwater. I'm Scott Manley. Fly safe.