HN Theater @HNTheaterMonth

⬐ douche

I will never be able to look at a video of a space flight again without thinking of how it would be achieved in Kerbal Space program.

Four Mk2R Radial Mount Parachutes, I think...

⬐ jewel

If anyone here hasn't played Kerbal Space program, try out the demo. It's less of a game and more of a space rocket simulator, with a real physics engine. I learned a lot by playing it.

I'm not in any way affiliated with the game, but can say with certainty that the overlap of HN readers and people who would enjoy the game is very high.

⬐ Florin_Andrei

Due to that game, I can talk with my 13 and 10 year old kids pretty casually about orbital mechanics, Hohmann orbits, etc. "Remember? This is just like that thing in KSP." ;)

⬐ david-given

This diagram says it all:

https://xkcd.com/1356/

⬐ kincardine

It's also less of a simulator and more of a total brain takeover.

When I first started playing all I could think about (as I was trying to get work done) were trans-munar injections and free-return trajectories.

⬐ stuxnet79

I bought the game but still haven't played it yet. How much of a timesink is it? Could it be enjoyed in 30min to an hour playing sessions?

⬐ Buttons840

Yes, you can leave the game in almost any state and then pick up where you left off later. The only exception is suborbital flights, but getting to orbit takes 3 to 5 minutes max.

⬐ douche

For the first couple hours, you're going to be reverting to launch/construction every five minutes anyway when you mess up and crash or realize you didn't build your rocket correctly to do what you want to do.

⬐ None

None

⬐ TrevorJ

First couple of hours? That's still how I play 90% of the time.

⬐ TrevorJ

I've had a lot of fun watching my poorly designed ship blow up in hilarious ways than I have actually getting to orbit, so I'd say yes, you can def get a long way in a half hour.

⬐ simonh

If you're disciplined yes, but there are some situations in which you can't save the game, such as whiled a vehicle is moving through an atmosphere (such as while flying a plane or landing a capsule) or while firing engines. It can't save while the current vehicle is experiencing acceleration other than gravity. So you can get stuck In the game during such activities for a little while.

⬐ vecter

I'd appreciate it if someone could explain to me how dangerous it is to use multiple parachutes instead of one. It sounds like it provides more reliability in case the one parachute fails, but it also seems there would be a risk of the parachutes becoming entangled. I personally have no understanding of the engineering or a sense of those risks.

⬐ krschultz

This was pretty low risk considering that they have been landing the cargo Dragon capsule under parachute for a few years now. The crew Dragon capsule probably has slightly different weight & balance characteristics but the system hasn't changed that much.

⬐ JshWright

There are a few changes with this parachute system. Notably, it uses 4 chutes, rather than 3 (which is the number used by the current cargo Dragon, and how many the Crew Dragon test article used for the pad abort).

All in all though, you're right, this was mostly just a checkbox that needed to get checked off.

⬐ ChuckMcM

Josh, do you know if is there anywhere that confirms the 204s ISP number for the superdraco thrusters? And what the fuel mass is for that?

EDIT: yes its a typo, I mean 240s

⬐ JshWright

I don't know of any source for that. Is 204s a typo of 240s? 204s would be awfully low for a Hydrazine engine (though I suppose it's possible they care a lot more about the TWR and have optimized for that).

⬐ ansible

Even an Isp of 240 is not all that high. This page:

http://www.astronautix.com/props/n2o4mmh.htm

Lists a bunch of engines that have Isp values in the 300 range.

SpaceX tends to optimize for total operational cost, rather than performance, so I wouldn't be surprised by the tradeoffs they've made to create a reliable and reusable system.

⬐ delibes

The citation for the wikipedia page (240s ISP) gives an exhaust velocity of 2,300m/s :

https://en.wikipedia.org/wiki/SuperDraco#cite_note-DragonFly... - page 12 of the PDF.

So taking a rough 2300/9.8 gives about 235s

⬐ irrelative

FWIW, Isp is measured in seconds and by multiplying it times gravity, you get the exhaust velocity. I believe this was done to more easily compare rocket efficiency regardless of units of gravity.

It looks like you're doing this calculation:

Isp * Gravity / Gravity

If you're trying to predict the hover duration, that will depend on the delta V of the vehicle. Then, a hover duration would be:

Delta v / Gravity

Not sure what the expected delta V is for the Dragon though.

⬐ ChuckMcM

Yes I read that (and the spaceflight insider article (http://www.spaceflightinsider.com/organizations/space-explor...), all numbers that are derived by third parties.

So while I do not doubt that the numbers for that vehicle and that test are accurate, I keep hoping to find actual data from SpaceX on the performance of the production rocket slated for use in the production Dragon Module.

I understand that SpaceX plays this information close to its vest given the competition with Boeing for Commercial Crew and perhaps Blue Origin should SpaceX ever decide to sell rockets for sub orbital tourist jaunts[1]. Anyway I'm just interested in more official specs so that I can have more confidence in my understanding of their capabilities.

[1] If you think about it, they have all the hardware, an F9r with a Dragon Crew mounted on top, they boost up to 100km, separate, the Dragon gets a nice ballistic arc for that weightless feeling and then both the booster and the capsule go back and land back at the pad for re-use.

⬐ sopooneo

Why do the parachutes chords angle to the side in the air? It seems like after a little while in constant wind, it would end up hanging vertically, while falling at an angle.

⬐ WatchDog

One side of the chord is shorter than the other.

⬐ lobster_johnson

Good, relevant discussion here: https://m.reddit.com/r/askscience/comments/3xs6mg/how_do_lar...

⬐ lmm

Needs [video] tag.

⬐ Tharkun

Youtube link: https://www.youtube.com/watch?v=4PG438XSarg

⬐ novlean11

SpaceX with their reusable stuff is definitely changing the whole space industry. We might have an option to fly out there in our life time without being a millionaires.

⬐ stuxnet79

Yes, I just finished Elon Musk's biography and it seems the objective is to get the price down to between $500,000 to a million for getting a single person to Mars. Extremely ambitious, but if it does happen, I will sell my house plus whatever hard assets I will own at the time and take my trip one-way to Mars.

⬐ JoeAltmaier

I'll be on that trip too!

⬐ ufmace

Why?

⬐ rebootthesystem

Sell your stuff, then move to Africa and start solving problems there. You can do that now. Probably harder than Mars yet far more rewarding and of immediate, long lasting and relevant benefit to humanity.

⬐ jernfrost

I thought a lot about that too. A lot of people think that seems nuts of course to move to such a barren hostile world. But there is a certain appeal to do something advances human civilization. On earth you are just one small cog on the big wheel. You don't matter that much to the well being of earth civilization. But on Mars every single colonist would matter a lot for the future of that colony.

Even if one dies earlier on Mars, it would seem better to live a short life with purpose than a long without purpose.

⬐ meric

What about Antarctica? Sure it's not a different planet, but you will be doing things that advance human civilisation and every person on Antarctica matters.

EDIT:

There's a lot of scientific research going on down there. [1]

In Antarctica you can participate in research that can reduce the possibility of such a catastrophe in the first place.

[1] https://en.wikipedia.org/wiki/Research_stations_in_Antarctic...

⬐ XorNot

What you can do in Antarctica is fairly limited (by international treaty) - unless you want front row seats for when the treaties run out in 2048.

⬐ outlace

How is living on Antarctica advancing humanity? That would just be living in barren cold for kicks. Building and sustaining a colony on Mars would pave the way for future space colonization and possibly prevent the human species from going extinct if a catastrophe happened on Earth.

⬐ adrianN

I regularly check job offerings in Antarctica, but the openings are few and the competition is fierce. I think you'll have a really hard time getting a job there unless you already work for an organization that does research there.

⬐ rglover

Slow, steady progress is a beautiful thing.

⬐ karanbhangui

I have a document I keep notes in for major life lessons or principles for myself. I've added your perfect quote under the principle for mastering the value of time and compounding: https://www.dropbox.com/s/4hdwbj0igcyivcd/Screenshot%202016-...

⬐ rglover

Ha! That's awesome, thanks for the inclusion :)

⬐ backtoyoujim

who owns washington post and spacex?

⬐ Ankaios

The Post is owned by SpaceX's competitor, Jeff Bezos.

⬐ ChuckMcM

The more interesting test for me was the hover tests (https://www.youtube.com/watch?v=07Pm8ZY0XJI) I keep doing back of the envelope calculations to see if a Dragon2 has enough fuel capacity to land and return from the lunar surface. Granted there is limited ability to leave and re-enter the capsule but it would make for an interesting capability.

If I recall correctly the "land on land" scenario for dragon has it using parachutes most of the way down, then doing a drop and land at the end.

⬐ skykooler

I don't think it can do so. The Dragon 2 has a delta-V of around 400 m/s, and lunar orbital velocity is around 1600 m/s - so you'd need at minimum 3200 m/s to land and take off again. The dragon would need to carry some sort of fuel+landing legs trunk to drastically increase its delta-v to even have a chance.

⬐ martythemaniak

I think Dragon 2 is a propulsive landing all the way, with parachutes used only in case of emergency. /r/spacex would be a good place to ask this (and the moon landing question), lots of people are quite knowledgeable and like running numbers like this.

⬐ mikeash

Dragon 2 is going to start out doing parachute landings with no propulsion at all. Once the system is sufficiently proven, they'll switch over to propulsive landings, where the parachutes are just an emergency backup in case the engines don't light or something.

⬐ sandworm101

Won't happen. Nasa will never do a purely propulsive landing of such a craft.

Parachutes cannot act as backup to a rocket-powered landing. Chutes need speed+altitude to deploy. If the rockets fail 25 meters above the ground, chutes won't save anything. If the craft has chutes+people on board, they will be deployed long before touchdown. Better out than in.

The only fully propulsive landing option, with humans on board, would be to have a second set of engines ready to perform what in an airplane would be called a zero-zero ejection maneuver[1]. This would see the craft reverse course, ascending rapidly to a trajectory where the chutes have time/energy enough to properly deploy. It would basically be a launch escape system. To keep that, and the chutes, and the descent engines ... just use the chutes. It isn't saving much money not deploying them as they will probably require repacking for inspection either way.

[1]A zero-zero ejection seat is one that can save a pilot from a craft parked on the runway, at zero-speed and zero altitude. Older seats required altitude and/or speed. But the dragon would be descending, with a negative alt/speed, so I guess this would be a sub-zero-zero ejection. A descent escape maneuver?

⬐ mikeash

Dragon 2 has full engine out redundancy for landing already. And even if that's not good enough for NASA, they probably won't be the only customers.

⬐ sandworm101

It has the reserves of engine power, but not a full separation of fuel and control systems. For human spaceflight they want to see a backup system that is dissimilar and disconnected from the failing system. So launch abort is a different rocket than that lifting the craft. For chutes, that's an extra chute stored in a different box. For propulsive landing, that would need to be separate rockets using separate fuel tanks controlled by a separate control system. Chutes will be lighter/cheaper.

⬐ tempestn

You make some useful points about the challenges. However, NASA will never do a purely propulsive landing of such a craft? Is it really inconceivable that over time it could become, and be demonstrated to be, at least equally safe to using parachutes?

⬐ sandworm101

Never isn't from a policy but a physics standpoint. If the chutes are already there, then it makes sense to use them. They are lighter/cheaper than hauling a full backup rocket system.

From what I've seen, it looks like SpaceX plans on using the rockets to cushion a landing already under chutes, like the russians do today. That allows for much smaller chutes and faster landing. If the rockets fail then the landing with be rough but still survivable, with the re-usability of the craft being written off.

The propulsive landing of booster stages makes sense only because you already have giant engine/fuel reserves, which aren't going to orbit. And since there are no humans around you don't need any sort of abort option.

Also, if you are going to have a potentially rough landing, would you rather do so sitting 6" from a box containing a parachute, or 6" from a tank of rocket fuel?

⬐ tempestn

> Also, if you are going to have a potentially rough landing, would you rather do so sitting 6" from a box containing a parachute, or 6" from a tank of rocket fuel?

The former, of course. I agree that a propulsive landing wouldn't be likely any time in the near future. But if it could eventually be shown to be safe (and therefore the quote above doesn't apply), I don't necessarily agree that it would be more expensive. You wouldn't need large engines or a lot of fuel, as the capsule wouldn't be very heavy. Yes, it would definitely still be more expensive than parachutes in terms of equipment and weight. However, it would mean you could land right back at your facility, rather than splashing down in the ocean and dealing with retrieval. When we're looking into the future of reusable, commodity space travel, that would be a significant advantage.

⬐ sandworm101

Why would a parachute not land at the home facility? Some, parafoils, can be flow and landed on runways like a glider. Nasa has been working on this concept for years. The X38 one was massive overkill, a full glider, but the concept of a chute directing the craft to a very specific touchdown point is well within today's tech.

http://spaceflight.nasa.gov/history/station/x38/parafoil.htm...

⬐ ansible

They also need the parachutes because if there is an emergency during launch, the thrusters will be used to separate the capsule from the launch vehicle.

They demonstrated this with their pad abort test:

https://www.youtube.com/watch?v=1_FXVjf46T8

Perhaps later this year we will also see an in-flight abort test, which will be very exciting.

⬐ dogma1138

IIRC NASA missions (at least initially) will use parachute landing while other missions will use propulsive landing. The propulsive landing engines serve in case of mission abort so they aren't wasted in any case, but as it's looking now NASA will not be trusting them for landings.

⬐ jordanthoms

Yep, Dragon 2 is capable of propulsive landing with no parachutes on earth, although to begin with it'll use parachutes and land in the water (perhaps using the engines to soften the landing).

Interestingly, Dragon 2 does have enough fuel to land on Mars, with clever aerobraking. NASA has done some feasibility studies on using a Dragon to land on Mars with a sample return vehicle inside it.

⬐ JshWright

Far more important than the parachutes is the atmosphere. Even without parachutes, the atmosphere is responsible for almost all of the deceleration the capsule experiences. The atmosphere takes it from orbital velocity (~30,000 m/s EDIT: ~8,000m/s (km/h->m/s conversion fail)) and slows it down to the terminal velocity of the capsule (~100 m/s). The capsule only has to take care of that last bit from terminal velocity down to 0 m/s.

On the moon, there is no atmosphere, so the capsule would have to handle all the deceleration from lunar orbital velocity (~2,000 m/s) to 0. So, in ballpark figures, you're looking at 20 times more 'delta V' (change in velocity) that the capsule would have to accomplish in order to land on the moon. It takes _way_ more fuel to manage that.

⬐ baq

if you replaced the dragon's trunk with a booster, it should be enough. i'm pretty sure it's not feasible, but in KSP world totally would work.

⬐ sathackr

obligatory https://xkcd.com/1244/

⬐ zardo

I doubt Falcon Heavy could throw enough mass to make it work. Dragon is just a poor vehicle to send to the moon. It should work for landing a few tons on Mars though (one way).

⬐ greglindahl

FH is 117 MT to LEO vs Saturn V 140 MT, Dragon is bigger/heavier than the Apollo capsule, and the even smaller LEM was the thing that landed on the Moon.

⬐ adwn

> FH is 117 MT

No, FH is advertised [1] as 53 mT to LEO (probably around 200x200 km, 28.5°).

[1] http://www.spacex.com/falcon-heavy

⬐ greglindahl

Sorry, pounds/kilograms brain fart on my part.

⬐ endymi0n

Nevertheless, quick back-of-the-envelope calculation should make an Apollo-style operation completely viable. Launch Dragon into orbit, Launch a fully loaded second stage without payload into orbit with a second FH and dock with the Dragon, Command Module style, then use the second stage for lunar orbit insertion and back. Should do the trick, even with a much heavier capsule.

⬐ JshWright

Using more than one launch is very much not an 'Apollo-style' operation. One of the major features of the Apollo program is that is used a single launch, which distinguished it from all the other competing proposals at the time.

⬐ hughes

30,000 m/s is several times the escape velocity of Earth... most orbits are close to 8,000m/s!

⬐ JshWright

Yep... km/h -> m/s conversion failure, thanks!

⬐ v0x

Having played a number of hours of Kerbal Space Program, I can verify that this information is correct.