Why have SpaceX, Boeing & Blue Origin ditched abort towers?

Video Statistics and Information

Video
Captions Word Cloud
Captions
- Hi it's me Tim Dodd, the Everyday Astronaut. There's a new trend going around in the commercial space industry when it comes to launch abort systems. All 3 commercial companies who are putting abort systems on their crewed vehicles have ditched that classic launch abort tower we've seen dominate abort systems in the past. Previous vehicles like The Mercury capsule, The Apollo capsule and even the Soyuz capsule all used an escape tower that sat on top of the crew module. Capable of pulling the vehicle away from a failing rocket in a hurry. And to make this topic even more interesting we're seeing another trend in abort systems. SpaceX's crew Dragon capsule and Boeing Starliner capusles, both are using liquid filled abort motors instead of solid rocket motors. So today we're gonna at talk about the design considerations that have made SpaceX, Boeing and Blue Origin ditch abort towers on their crewd vehicles and we're also going to re-evaluate why the heck are Boeing and SpaceX going with liquid rocket motors instead of solid rocket motors. And with both SpaceX and Boeing having experienced serious setbacks and complications with their liquid fueled abort systems including the loss of a test vehicle. It raises the question, is it even a good idea? Now there's a lot of fun engineering decisions behind each and every system, so lets get started. (upbeat music) I've talked about abort systems quite a bit in the past. I have a video explaining why SpaceX's Crew Dragon capsule has fins on the trunk. Which helped keep it pointy and up and flamey and down in the even of an abort. And I have another video talking about why the gemini capsule went with an ejection seat instead of a launch abort tower. So for a short run through on mechanical abort systems, here's a brief overview. If you're sitting on top of a skyscraper full of explosive materials it's generally considered a good idea to have a way to evacuate quickly if things go wrong. The way abort systems originally worked was by having a trail of wires running down the entire length of the tanks of the rocket. If any two of them are severed it triggered an abort system to fire up the motors and detach the crew module within a fraction of a second. The abort motors have to be powerful enough to pull the vehicle away from a failing rocket as quickly as possible. These systems can pull up to 15g's of accelaration for a few seconds. Now I'm not saying that sounds like fun but that actually sounds awful. It sounds like been hit by a semi-truck for a few seconds continuely, yeah no thanks. And since the very beginning of human space flight well atleast in the United States, engineer's opted for a launch escape tower stuck on top of the capsule. You'll notice some fancy scafollding with a few really powerful rocket motors attached to it. On top of the Mercury Capsule, the Apollo capsule. The Soyuz capsule, China's Shenzhou capsule as well as the upcoming Orion capsule and India's Gaganyaan capsule. All of these vehicles also used solid rocket motors in the abort system because solid rocket motors are very powerful for their size. They can be lit in an instant. They're simple and are relatively safe to have sitting around idle. This configuration with a tower is called a tractor of a puller system. Since the motors are in front of the vehicle and they pull the vehicle free as opposed to most rocket motors which are at the bottom end of the vehicle and they push it. The three newest capsules that will be carrying humans to space have opted to ditch the tractor abort systems and go with a different approach called a pusher system. And even more interestingly SpaceX, Boeing and Blue Origin all have wildly different reasons for doing so. So let's start off with Blue Origin and their New Shepard capsule. New Shepard is one of two players in the sub-orbital tourism game. Competing with Virgin Galactic and their Spaceship To Space Plane but Blue Origin's New Shepard is the only one of these two that offers an abort system. The abort system that Blue Origin decided to go with is solid rocket motor placed smack in the middle of their capsule underneath what looks like a beautiful table but is actually a large chunk of blast resistant and high pressured tubing holding the solid rocket motor. As mentioned before this makes it a pusher system since the exhaust comes out of the bottom of the vehicle when used during an abort. Now an interesting note with this system is how wobbly it looks when in use. This is likely because the center of thrust is very close to the center of mass making it inherently less stable. I talked about this briefly in the video about why the Crew Dragon capsule has fins on the trunk. Saying it looks like New Shepard could use some aero-services to help keep it more stable but then again as long as it get's the heck out of there, it's probably fine. Blue Origins use of a solid rocket booster makes sense for this abort system. Since it's only to be used in emergency. It just kinda hangs out there hoping to never need to be used. Something a solid rocket motor does perfectly. It's high thrust to weight ratio and safe storage makes it a no-brainer for this. So now we can ask ourselves, why didn't they go with a more traditional escape tower? First off, The New Shepard is trying to operate as inexpensively and frequently as possible by being fully re-usable. It's booster very impressively lands itself propusively and the capusle relies on safe and reliable parachutes to make a soft touchdown. The name of the game is little to no refurbishment. A lauch abort tower is traditionally jettisoned once it's useful window of operation has passed to free up dead weight from the vehicle but with a sub-orbital system that only goes straight up and straight back down. You'd think they'd probably just keep the tower on. And this is espcially true since there's no docking port that would need to be uncovered because their New Shepard vehicle doesn't dock with anything but say you did leave it on, it's pretty safe to say you wouldn't wanna deploy your parachutes in the vicinity of that launch escape tower because there'd be a pretty big risk of them getting tangled up in it. So in the case of a launch abort tower mission success relies on that tower being ditched or else the parachutes won't work correctly. So that raises the question, is it better to design a system that requires a separation event every single flight in order to be successful? Or do you wanna design a system that only needs to be used in an emergency? And besides that Blue Origin wouldn't want to ditch the abort tower and flight since it could land pretty close to their facilties and it would be likely destroyed with each and every flight, which would add to the cost but there's perhaps even a bigger reason why Blue Origin went with pusher system. And by bigger, I mean bigger. Take a look at these puller systems. Do you notice anything missing? Puller systems almost always have a protective faring or a shell that covers the windows and the rest of the vehicle to protect the vehicle if the abort system is used. It'd generally be a good idea to make sure your windows are covered up so you don't completely oblitirate them. The Mercury capsules had a window and an escape tower but on the Mercury capsule the motors were much higher up on the tower than other systems. And we did things a little differently in the early days of human space flight that might just be frowned upon today. Since puller abort motors and windows don't typically go hand in hand, covering up world's largest windows that go to space would be a pretty big shame. Since New Shepards entire purpose is to provide the ultimate tourist experience with stunning views. They sure wanna make sure seeing out those big, giant, beautiful windows is a top priority. So for Blue Origin the use of a pusher type solid rocket motor abort system makes the most sense. Next up, let's talk about Boeing's Starliner and SpaceX's Crew Dragon Capsules which both were designed for NASA to send crews up to the International Space Station. Now these are purpose built taxis to the ISS first and foremost although both vehicles may seek commercial use someday for private customers. I have a video that dives really deep into both of these vehicles and the rockets they ride on and then I compared them to the space shuttle and Soyuz, the other vehicles that visit the ISS. So if you need a rundown on what the history is. The specs and all of the considerations of these vehicles, definetely check this video out. Both SpaceX's Crew Dragon capsule and Boeing's Starliner opted to use a pusher system too. They've chosen to ditch the tower but both of these cheicles opted to use liquid fueled abort motors instead of the more traditional solid rocket motors. Now you might be thinking, how can a liquid fueled rocket engine be quick and safe enough to be relied upon for an emergency abort. After all, rocket engines can take several seconds to get the pumps spinning and for ignition to occur so that doesn't really sounds like a good option. Well, these liquid fueled rocket engines are using a similar system to what's used in reaction controlled systems which offer very quick and reliable ignition. They do this by using utilizing a pumpless rocket engine known as a pressure fed engine. Pressure fed engines just have their propellants stored in a very high pressure tank. They open a valve and they let it rip. And to make it even more reliable the pressure fed engines used on these abort motors run on hypergolic propellants. Hypergolic propellants burn on contact with each other so there's no need for a secondary ignition source like a spark or a flame. This makes the pressure fed hypergolic engine very simple, quick acting and reliable. A great choice for reaction control and abort motors. It should also be noted that although hypergolic fuels are very stable and reliable, they're incredibly toxic, Cancerogenic and just really nasty stuff. So why did both companies choose liquid fueled abort motors? There's a few reasons but first and foremost it's likely due to increased safety requirements from NASA. They wants what's known as fuel envelope abort system or the ability to abort safely from any point in the flight. Now solid rocket motors can provide this option too. For instance, the Orion capsule solid rocket tractor system offers an abort mode for the first two minutes of flight after which the tower is jettisoned and the second stage of the SLS system or the service modules AJ 10 engine can provide abort options. But with liquid fueled abort motors they can fire them for less time or lower thrust than a solid rocket motor which gives them the ability to place the vehicle precisely into a desired trajectory to either re-enter safely or abort to orbit. Which can make it easier to design a full envelope abort window. But quite frankly each company could have gone with a typical tractor solid rocket motor abort system. As a matter of fact, SpaceX's original concepts for the Crew Dragon capsule or Dragon Rider as they called it back then was going to utilize a traditional tower and then jettison it on ascent as we can see in this animation from 2010. So the first reason each company opted for a pusher system is the same reason we talked about before. By removing a separation event, you're eliminating a potential mission failure scenario. By intergrating the abort system into the vehicle it simplifies sequence of events needed for mission success. But intergrating the abort system doesn't necasarily mean they have to use liquid fuels, does it? I mean, New Shepard get's away with it. Well there's two reasons why utilizing liquid fuel abort motors in these cases are actually more useful or even necessary in an integrated abort system. The first reason is control. Liquid fuel rocket motors can steer and point the vehicle by doing something called thrust differential which is where they can increase or decrease thrust on any of the motors and that can help point it in the correct way. This definetely helps keep the pointy end up and the flamey end down. Now there are ways to control a solid rocket motor but thrust differential isn't one of them. So in order to steer a solid abort tower one cool way is by having a seperate solid motor fire and having multiple valves open and close on each side of the tower. Take a look at this Orion attitude control motor test. Inside there is a solid rocket motor that lights and cannot be turned off once activated but in order to provide steering, they can vary how much thrust comes out of any of it's eight valves. To provide neutral input they just open up all eight valves equally which then will produce no change in direction. They then stick this unit really high up on the abort tower to provide maximum leverage over the vehicle which helps provide ample control during the abort. I think this is really cool. In a pusher system there's no tower to provide leverage so you can't put control services up there. So using a solid rocket motor that can't provide thrust differential can be a bit of a no-no. But there's actually another reason why you can't use solid rocket motors on these two vehicles. And that's because these vehicles visit the International Space Station and because they visit the International Space Station the abort motors also visit the station. This means 32 times a day the vehicle has extreme changes in temperature or thermal cycles. Now hypergolics are happy as a clam and stable hanging out in these conditions. As a matter of fact, there's hypergolics on the station as we speak. The thermal cycling of a rocket motor that much could potentially lead to some unintended booms. And that's definetely not a good thing when you're attached to the single most expensive piece of machinery with precious human lives on board. So why are they even bothering intergrating the launch abort system at all? This all sounds like an awful lot of trouble. Besides the simplicity of an integrated system not needing to separate, the two companies actually have very different reasons for their integration. Boeing modified some Aerojet Rocketdyne RS-88 Bantam motors to run on the same fuel as the reaction contol system that is part of the service modules Starliner instead of the alcohol and liquid oxygen they normally use. The service module also houses the solar panels and radiators of the vehicle. By using the same fuel for the abort and the reaction control systems it means an anominal mission the abort system obviously isn't utilized which means the extra propellent can be used for other things. Besides having more fuel for orbital maneuvering you also end up with spare propellent to potentially reboost the International Space Station. Now this is something only Russia's Progress supply vehicle and the Signis cargo vehicle can currently do. But the retired space shuttle and the ATV vehicle could also do it previously. Having the ability to reboost the station is definetely a nice selling point. Although we don't have any confirmation on whether or not Starliner will ever perform this maneuver but atleast having it is isn't a bad option at all. But for SpaceX, perhaps their biggest reason why they didn't wanna ditch their motors is 'cause they designed the Dragon capsule to be reused as much as possible. This means by integrating the abort motors with the capsule itself, they would recover them with each flight. But ironically the Dragon capsule is less reusable than the Starliner since the Crew Dragon capsule splashes down as opposed to the Starliner which will land on land. This means that the Crew Dragon capusle will never be never be reused for crew and will only be used as a cargo vessel. And what's even more ironic is the Starliner which lands on land and can be reused up to 10 times ditches it's abort motors with each and every flight. As the service module which houses the abort motors is jettisoned before re-entry. So the vehicle which lands on land ditches it's abort motors and the one that lands in the ocean keeps it's abort motors. That's interesting but the main reason why SpaceX's Crew Dragon has the super Draco liquid fuel abort motors in the first place isn't just for abort options. They originally intended to land the Dragon capsule propulsively. Yes that's right, they originally intended to land the Dragon Capsule much like SpaceX lands it's Falcon9 and Falcon Heavy Rockets. Riding pillars of flames, so cool. Now the original reason for landing propulsively was for rapid and easy reuse of the vehicle. Not only that but they also wanted the Dragon capsule to land on Mars. SpaceX's original goal with the Dragon was to land it on Mars for a mission dubbed Red Dragon but the whole propulsive landing idea got scrapped. SpaceX gave up on pursuing propulsive landing with the Dragon capsule mostly because NASA really wasn't interested in the concept. As it would require far too much additional work to certify. So now that we've talked about why each company ditched the tower and why both Boeing and SpaceX has opted to use liquid fuelled propellent's for it's launch abort systems. It raises the question, is it even a good idea? Both Boeing and SpaceX have had problems when testing their liquid abort systems. Boeing experienced an anomily with a Starliner test vehicle in 2018 when preparing to do a pad abort test, where the hypergolic fuels leaked out of the vehicle. SpaceX had something a little more energetic happen in 2019 when preparing to do a static fire test prior to an in-flight abort test with their recovered DM-1 Crew Dragon capsule. In my opinion these issues will get worked out. These fuels using these systems are the same or very similar to almost all orbital spacecraft. After all, satellites often use hypergolic fuels and a liquid motor to do their orbital maneuvering. The space shuttle had hypergolic fuels for it's orbital maneuvering system and hypergolics are already used on Dragon-1 for well over a dozen missions. And there rarely has been any issues with these systems. In general these systems can be safe, simple and reliable. So why are we seeing such major problems arise when testing them? Well the public relation answer is, that's why we test. But I kind of have a feeling it has to do with how you test this stuff. You often times go beyond what you'd normally be doing. And doing things in these testing campaigns that wouldn't normally be done on the launch pad. As far as is it a good idea, I mean I think so. The fuels are already on the vehicle in the first place so it makes sense to use them for a launch abort system. Liquid fueled abort systems are useful. Potentially reusable and actually make for a simpler spacecraft and mission profile. Not to mention, when they're not used they can be utilized for other purposes such as reboosting the ISS or even propulsively landing. Although we probably won't ever see either of those things happen. I'm sure each company is learning from the failures of these systems and I have little doubt this will all be sorted out before we ever put humans on board. And hopefully that's sooner rather than later. So it is interesting that we went from one common form of launch abort to suddenly three 21st century companies using widly different systems. But in the long run each company has a unique reason behind their engineering decisions. Which I find fun. So does this help answer your questions of why companies have scrapped abort towers? Or why they're now using liquid fueled rocket motors? Let me know if you have any other questions about this topic in the comments below. In keeping with this trend of talking about escape systems, I plan on making a video about why SpaceX doesn't plan to use an abort system on their upcoming Starship and help answer the question of whether or not that's a good idea. I owe a huge thanks to all my patrion supporters for helping me make videos like this and all other content possible. Patrion members get exclusive access to a sub-Reddit and a Discord channel as well as excluive live-streams and early access to some videos. So if you wanna help support what I do please head on over to patrion.com/everydayastronaut. And while you're online be sure to check out my web store for lot's of fun new merchandise such as Gridfin coasters, hats like this. Prints, maybe t-shirts like this. Lots of other fun stuff at everydayastronaut.com/shop. As always, all the music in my videos is original and you can listen to some of my music on Spotify or iTunes or Amazon or Google Music. Or really wherever you listen to music. For easy links, got to everydayastronaught.com/music and share it with a friend. Thanks everybody, that does it for me, I'm Timm Dodd. The Everyday Astronaught bringing space down to earth for every day people. (upbeat music)
Info
Channel: Everyday Astronaut
Views: 1,035,164
Rating: 4.8827739 out of 5
Keywords: spacex anomaly, dragon capsule explosion, spacex dragon explosion, abort tower, why liquid abort motors, spacex abort motors, spacex abort test, spacex abort motor test, spacex abort motor test problem, spacex test problem, spacex lost dragon, spacex explosion, boeing abort motors, boeing abort test, boeing abort problem, liquid escape motors, solid rocket motors, pusher abort motors, pusher escape system, tractor escape system, how do abort motors work, everyday astronaut
Id: 0MaeHNU2660
Channel Id: undefined
Length: 19min 27sec (1167 seconds)
Published: Thu Apr 25 2019
Reddit Comments

With the ongoing investigation of the SuperDraco static fire anomaly, I got asked a lot of really good questions surrounding the use of hypergolics as an abort system. This led to some really interesting rabbit holes. It should be mentioned that I talk about thermal cycling of solids on orbit, and should bring up Soyuz which has those soft touch down motors, but unlike an abort system, they aren't inherently exposed and can be well insulated deep inside the capsule until their use. For those of you that can't watch a video, here's an article version as well. Thanks for the great questions and thanks for the feedback / and help with research! Lots more videos coming, this next set is the craziest script I've written, so I hope you enjoy my deep rundown on the Raptor engine!

👍︎︎ 521 👤︎︎ u/everydayastronaut 📅︎︎ Apr 25 2019 🗫︎ replies

Great video Tim. I know you've been hard at work on this and several others coming up. While I had a general idea of the differences between the various abort systems this vid did a great job of laying it all out clearly. Let's hope both Boeing and SpaceX can figure out their issues and get back on track soon.

👍︎︎ 72 👤︎︎ u/inoeth 📅︎︎ Apr 25 2019 🗫︎ replies

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters More Letters
ASDS Autonomous Spaceport Drone Ship (landing platform)
BFR Big Falcon Rocket (2018 rebiggened edition)
Yes, the F stands for something else; no, you're not the first to notice
BO Blue Origin (Bezos Rocketry)
CCtCap Commercial Crew Transportation Capability
CRS Commercial Resupply Services contract with NASA
CST (Boeing) Crew Space Transportation capsules
Central Standard Time (UTC-6)
DoD US Department of Defense
Isp Specific impulse (as discussed by Scott Manley, and detailed by David Mee on YouTube)
IRFNA Inhibited Red Fuming Nitric Acid, mixed with hydrogen fluoride for stability
ISRU In-Situ Resource Utilization
ITS Interplanetary Transport System (2016 oversized edition) (see MCT)
Integrated Truss Structure
LEO Low Earth Orbit (180-2000km)
Law Enforcement Officer (most often mentioned during transport operations)
LES Launch Escape System
LOX Liquid Oxygen
MCT Mars Colonial Transporter (see ITS)
MMH Mono-Methyl Hydrazine, (CH3)HN-NH2; part of NTO/MMH hypergolic mix
NTO diNitrogen TetrOxide, N2O4; part of NTO/MMH hypergolic mix
RCS Reaction Control System
RP-1 Rocket Propellant 1 (enhanced kerosene)
SRB Solid Rocket Booster
STP-2 Space Test Program 2, DoD programme, second round
STS Space Transportation System (Shuttle)
mT Milli- Metric Tonnes
Jargon Definition
Raptor Methane-fueled rocket engine under development by SpaceX, see ITS
bipropellant Rocket propellant that requires oxidizer (eg. RP-1 and liquid oxygen)
cryogenic Very low temperature fluid; materials that would be gaseous at room temperature/pressure
(In re: rocket fuel) Often synonymous with hydrolox
hydrolox Portmanteau: liquid hydrogen/liquid oxygen mixture
hypergolic A set of two substances that ignite when in contact
methalox Portmanteau: methane/liquid oxygen mixture
monopropellant Rocket propellant that requires no oxidizer (eg. hydrazine)
Event Date Description
CRS-1 2012-10-08 F9-004, first CRS mission; secondary payload sacrificed
CRS-2 2013-03-01 F9-005, Dragon cargo; final flight of Falcon 9 v1.0
DM-1 2019-03-02 SpaceX CCtCap Demo Mission 1

Decronym is a community product of r/SpaceX, implemented by request
28 acronyms in this thread; the most compressed thread commented on today has 78 acronyms.
[Thread #5113 for this sub, first seen 25th Apr 2019, 14:10] [FAQ] [Full list] [Contact] [Source code]

👍︎︎ 23 👤︎︎ u/Decronym 📅︎︎ Apr 25 2019 🗫︎ replies

Crew Dragon Capsule will never be reused for crew and will only be reused as a cargo vessel.

Tim, do you have a source for this? Both NASA and SpaceX confirmed pursuing certification for used and splashed down Dragon 2 is possible and that SpaceX didn't pursue it because they don't find it a good use of their time.

Propulsive landing is better for rapid reuse than splash down, and that's why they were after it in the first place, but I have never seen other claims that it was required.

👍︎︎ 12 👤︎︎ u/minimim 📅︎︎ Apr 25 2019 🗫︎ replies

Recent videos from Everyday Astronaut have been very high quality. Well paced. Good visuals and explanations. Well written and researched. I like where he is going with his Youtube content.

👍︎︎ 11 👤︎︎ u/shirro 📅︎︎ Apr 26 2019 🗫︎ replies

Could you please make a video on the starliner? Some of it's features like solar panels on bottom and the large command seat window are really interesting. It'll be a great video and also give some love to Boeing. Their capsule doesn't get nearly as much attention as the dragon.

👍︎︎ 49 👤︎︎ u/oximaCentauri 📅︎︎ Apr 25 2019 🗫︎ replies

As always, enlightening, well-written, and a pleasure to watch. Thanks, Tim!

👍︎︎ 7 👤︎︎ u/Paper_Kosmonaut 📅︎︎ Apr 25 2019 🗫︎ replies

Is there not another fuel source other than hydrozine or whatever they are using now that is not as dangerous?

👍︎︎ 4 👤︎︎ u/MagnasisTV 📅︎︎ Apr 25 2019 🗫︎ replies

Dang, Tim. Your videos are just getting better and better. It's great to see your video production improve over the years. Thanks for all the time and effort you put into educating us.

👍︎︎ 3 👤︎︎ u/sir-shoelace 📅︎︎ Apr 26 2019 🗫︎ replies
Related Videos
Note
Please note that this website is currently a work in progress! Lots of interesting data and statistics to come.