An astronaut explains how it'd feel to ride Elon Musk's giant spaceship

[Ben W]

As I said, there would be no good reason for a manned rocket launch vehicle to accelerate that fast. It would be highly wasteful to equip it to do so. 0.25 G's of acceleration for the Apollo/Saturn V at liftoff sounds about right. Playing around with the acceleration vs distance formula, I get approximately 0.32 G of acceleration for the Space Shuttle in the first 6 seconds after liftoff, which of course means ~1.32 G experienced by the Shuttle astronauts at liftoff.

It looks like the truth may be somewhere in the middle. From this graph of the Shuttle acceleration profile, it looks like it starts off around 1.5G's:

https://i.stack.imgur.com/Q7ODR.png

Gravity losses are the most extreme during the first minute of flight, so faster acceleration (all else being equal) would be better. If magical boosters existed that could accelerate BFR at 3G's off the pad for the first 15 seconds or so, that would be fantastic. (How about a vertical railgun?) For a single stack though, since the G's are limited for structural reasons (sometimes requiring throttle-down or partial engine cutoff midway), you'd quickly be carrying a lot of engine dead-weight if you lifted off accelerating anywhere near the max. And Max-Q limits the velocity through transsonic, so a 3G launch couldn't be sustained for more than that 15 seconds or so without throttling back. The lower G-forces (and thus lower stresses) at launch also decrease the probability of a pad-destroying RUD.

For Falcon Heavy, the optimal performance profile would be to fire the side boosters at 100% at launch with the center booster throttled back to ~80%, to conserve more fuel for after booster separation. But structurally, it may be safest to reverse this for the first few seconds of launch (e.g. 80% side boosters, 100% center) to decrease shear stresses in order to reduce the chance of RUD until the vehicle is safely clear of the launch site. I'm curious if SpaceX is actually planning to do this, even if just for the maiden launch.

 

[daniel]

The "Vomit Comet" got its name for a reason, and it gives you 45 seconds of weightlessness at a time. If even 5 minutes of that BFR 20 to 30 minute flight are in microgravity, a lot of passengers are going to be using the barf bags, and probably some will fail to get the bag out in time, resulting in a lot of horrid messes for the flight attendants to clean up.

Would I ride the BFR? It would be tempting to reduce a 12-hour flight to Australia, or an 18 hour flight to the Far East to a mere half-hour. But I'd wait first and see what people say after they've flown on it. I get motion-sick easily, and can well imagine this being worse than a long trip on a cramped airplane.

And getting the price down to that of a commercial jet seems far-fetched.

 

[Doug_G]

Having done the 18 hour flights before, I’d take a < 60 minute flight even with some discomfort.

And I’d be wanting to do it just for the experience!

 

[daniel]

Having done the 18 hour flights before, I’d take a < 60 minute flight even with some discomfort.

And I’d be wanting to do it just for the experience!

For folks who don't get motion-sick, or just a little, I agree. And of course the experience would be amazing, though in spite of what Elon says, I don't think very many of us will be able to afford it. But for people who get motion sick, I can tell you, when it's bad, you really wish you were dead. And weightlessness, by all accounts, is the worst kind of motion sickness. I'd happily endure "some discomfort." But I envy you if the worst you get from motion is "some discomfort."

 

[Doug_G]

It would be over quickly. It’s not like being stuck on a heaving ship for days with no end in sight. Five minutes of puking into a bag wouldn’t dissuade me. (Unlikely to happen to me though.).

 

[Etna]

So true. "Vomit Comet" comes to mind.

Many people who experience weightlessness in ballistic fights for just a minute are throwing up. And it has cascading effects, if I dare to use the term.

I suppose one can get used to it after a few flights. Personally I'll be happy to trade a barf bag against an ultra-long-haul torture in economy, but probably not ultra-long-haul business class which provides a break that I actually enjoy (sometimes one needs to slow down for a few hours).

 

[N5329K]

It would be over quickly. It’s not like being stuck on a heaving ship for days with no end in sight. Five minutes of puking into a bag wouldn’t dissuade me. (Unlikely to happen to me though.).

Designing materials and systems to deal with multiple expanding clouds of zero-G passenger puke should keep the SpaceX engineers from getting bored any time soon.
Robin

 

[dhanson865]

So true. "Vomit Comet" comes to mind.

Many people who experience weightlessness in ballistic fights for just a minute are throwing up. And it has cascading effects, if I dare to use the term.

I suppose one can get used to it after a few flights. Personally I'll be happy to trade a barf bag against an ultra-long-haul torture in economy, but probably not ultra-long-haul business class which provides a break that I actually enjoy (sometimes one needs to slow down for a few hours).

People keep bringing up the vomit comet without realizing it's not the same.

It’s one parabola. And when we’ve seen people, for example, when they go on rides on NASA’s “Vomit Comet”… What we’ve seen from those types of parabolic flights is that people – if they get sick – its parabola six, seven, eight. It’s a delayed effect, really.

So you take SpaceX its one simple arc, it's not a sine wave like the vomit comet. You aren't going to throw up just from being weightless once in a simple flight.

 

[s0schen]

Got a couple incentive rides in a trainer F-16 many years ago as well a participating in centrifuge training that summer. The speed at which the G-forces are applied seemed to make a big difference. We were scared to death by the centrifuge since the instant application of G forces were pretty brutal and actually quite painful. A bunch of us passed at at just 6 G's if we didn't breath with right technique or tighten all the muscles in our legs just right. Then in comparison when we actually got the rides, the much more gradual build up of 6 or even 9 G's in the plane felt like a cake walk in comparison.

I bet the negative G's may actually be more a problem when returning and people "red out" when too much blood rushes to the head and venous return issues ensue if the duration is too great.

 

[Ben W]

I bet the negative G's may actually be more a problem when returning and people "red out" when too much blood rushes to the head and venous return issues ensue if the duration is too great.

The spacecraft will reorient itself for reentry so that there is never a "red out" condition (negative G's on the passenger). Relative to the ship itself, the forces of liftoff and reentry are roughly at right angles to each other. I imagine the seats would recline or swivel in such a way that the passenger is always "lying down" relative to the perceived acceleration.

 

[Todd Burch]

With passengers lying on their backs, liftoff and landing forces will always be primarily back to front from the passenger's perspective. As a result passengers will not experience significant positive (pushing from feet toward head) or negative (pushing from head toward feet) g forces.

 

[s0schen]

With passengers lying on their backs, liftoff and landing forces will always be primarily back to front from the passenger's perspective. As a result passengers will not experience significant positive (pushing from feet toward head) or negative (pushing from head toward feet) g forces.

Thanks. Agree. Forgot about the seat position.

 

[ecarfan]

There has been a lot of commentary in this thread about how a large percentage of passengers are likely to become nauseous and vomit in the microgravity phase of the flight.

Here is what I would like to know, not having experienced microgravity myself*; is the likelihood of microgravity-induced nausea significantly lessened if one is firmly secured in the seat for the duration of the approximately 30 minute flight?

It seems likely that E2E BFR passengers will be in seats that place them in a partially reclined position with legs slightly up and knees bent. Before launch, when in their seats, passengers will be oriented such that they consider the “floor” to be what is behind them. Launch will reinforce that perception since they will feel pressure on their bodies towards the “floor” similar to what we have all experienced every day of our lives.

And then the engines will cut off, the BFR will be in coast phase for something like 20 to 50 minutes, and passengers will be in microgravity but firmly restrained (in my opinion there is no chance in the early days of such flights that anyone will be allowed out of their seat, for a variety of reasons). Passengers will be able to turn their head and that will activate their vestibular system in a way that they are not used to (inertial fluid shifts in the absence of “normal” gravitational forces) but their visual system may continue to give them a solid “floor” reference. Of course that will result in a differing perception of “up vs. down” between the visual system and the vestibular system and that is what creates the problem we are discussing.

I’ve searched online for information about this — does staying firmly restrained during a short period of microgravity reduce the likelihood of motion sickness — but can’t find anything relevant to my specific question.

This article is interesting but does not address my question. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2696527/

This article says “Symptoms have their onset from minutes to hours after orbital insertion. Excessive head movement early on-orbit generally increases these symptoms. ” Space adaptation syndrome - an overview | ScienceDirect Topics

This article says “Immediately upon exposure to microgravity, certain physiological systems exhibit altered function. Many of these are associated with maintaining moment-to-moment homeostasis and/or are directly affected by the physical effects of microgravity. Examples of these are the baroreceptor reflex, neurovestibular system, and gastrointestinal tract.” https://www.faa.gov/about/office_or...al/media/III.1.1_Exposure_to_Microgravity.doc

But my question remains: if you are firmly restrained during a short period of microgravity (i.e. minutes, not hours) does that significantly reduce the likelihood of nausea compared to if you are floating freely?


*I have spent a lot of time scuba diving, which is a kind of weightlessness, but hardly the same thing as microgravity.

 

[oneday]

There has been a lot of commentary in this thread about how a large percentage of passengers are likely to become nauseous and vomit in the microgravity phase of the flight.

Here is what I would like to know, not having experienced microgravity myself*; is the likelihood of microgravity-induced nausea significantly lessened if one is firmly secured in the seat for the duration of the approximately 30 minute flight?

It seems likely that E2E BFR passengers will be in seats that place them in a partially reclined position with legs slightly up and knees bent. Before launch, when in their seats, passengers will be oriented such that they consider the “floor” to be what is behind them. Launch will reinforce that perception since they will feel pressure on their bodies towards the “floor” similar to what we have all experienced every day of our lives.

And then the engines will cut off, the BFR will be in coast phase for something like 20 to 50 minutes, and passengers will be in microgravity but firmly restrained (in my opinion there is no chance in the early days of such flights that anyone will be allowed out of their seat, for a variety of reasons). Passengers will be able to turn their head and that will activate their vestibular system in a way that they are not used to (inertial fluid shifts in the absence of “normal” gravitational forces) but their visual system may continue to give them a solid “floor” reference. Of course that will result in a differing perception of “up vs. down” between the visual system and the vestibular system and that is what creates the problem we are discussing.

I’ve searched online for information about this — does staying firmly restrained during a short period of microgravity reduce the likelihood of motion sickness — but can’t find anything relevant to my specific question.

This article is interesting but does not address my question. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2696527/

This article says “Symptoms have their onset from minutes to hours after orbital insertion. Excessive head movement early on-orbit generally increases these symptoms. ” Space adaptation syndrome - an overview | ScienceDirect Topics

This article says “Immediately upon exposure to microgravity, certain physiological systems exhibit altered function. Many of these are associated with maintaining moment-to-moment homeostasis and/or are directly affected by the physical effects of microgravity. Examples of these are the baroreceptor reflex, neurovestibular system, and gastrointestinal tract.” https://www.faa.gov/about/office_or...al/media/III.1.1_Exposure_to_Microgravity.doc

But my question remains: if you are firmly restrained during a short period of microgravity (i.e. minutes, not hours) does that significantly reduce the likelihood of nausea compared to if you are floating freely?


*I have spent a lot of time scuba diving, which is a kind of weightlessness, but hardly the same thing as microgravity.

I would wager a guess that it would help quite a bit. My experience with micro gravity has only been during brief stints (10 - 30 ish secs) as an aerobatic pilot. Even with a very gradual transition to micro gravity and being in a 4 point harness it is an unmistakable feeling. And you can really feel it in your stomach, it is slightly uncomfortable.

I am fortunate to be completely immune from motion sickness. I share that trait with maybe 5% of the population. I think peoples tolerance to motion sickness resembles a bell curve. I would wager there is at most 10% of the population who would get instant sickness from a 30 min Flight, roughly 10 of which is in microgravity. Those people would possibly not even be helped by things like ginger pills, Dramamine, scopolamine etc. The other 90% would be able to take ginger pills, Dramamine, scopolamine etc and be fine in my opinion (obviously just a guess).

I have demonstrated microgravity to over 100 people. Only 1 person ever puked in the plane. Maybe 10% told me they could take no more. And another 20% said they felt lingering nauseousness. And maybe another 30% felt slightly nauseous. I certainly didn’t perform any kind of study this is just my experience.

This is from Wikipedia:

According to former Reduced Gravity Research Program director John Yaniec, anxiety contributes most to passengers' airsickness. The stress on their bodies creates a sense of panic and therefore causes the passenger to vomit. Yaniec gives a rough estimate of passengers, that "one third [become] violently ill, the next third moderately ill, and the final third not at all." Vomiting is referred to as "ill".[10]

On commercial flights offered by Zero Gravity Corporation, very few passengers [33][non-primary source needed] experience motion discomfort. This is because the Zero Gravity Corporation's flights are much shorter than NASA's flights.

Scopolamine is often used as an antiemetic during reduced-gravity-aircraft training.

 

[oneday]

I have a seperate question. The original post by OP said that the BFR would experience up to 5g’s.

Is it group consensus that this is just plain wrong? That SpaceX will fly a profile that will never exceed 2g’s? Didn’t Elon say in the AMA that takeoff and landing will be 1.3 g’s?

 

[Etna]

Plain wrong indeed.

@dhanson865 pointed out in post #25 of this thread that Elon Musk tweeted that max acceleration would be 2 to 3 g's.

 

[oneday]

And that tweet was before the most recent AMA where he said takeoff and landing is 1.3 g’s.

Do we think BFS can achieve 3g’s with aerobraking alone? Would max force be before meco, some kind of retro burn or during aerobraking, anyone hazard a guess?

 

[dhanson865]

And that tweet was before the most recent AMA where he said takeoff and landing is 1.3 g’s.

Do we think BFS can achieve 3g’s with aerobraking alone? Would max force be before meco, some kind of retro burn or during aerobraking, anyone hazard a guess?

Max Gs would likely be after max Q just before the first stage engines cut off (depending on if they run them at 100% throttle after Max Q and/or how smoothly they throttle down before stage 1 engine shutoff and stage separation).

The biggest fuel wasted to gravity losses are on the way up so they'll have more incentive to use max thrust going up than to use high thrust on the landing phase. The further through the flight the less it will cost them to smooth out the ride.

 

[jkn]

People keep bringing up the vomit comet without realizing it's not the same.

It’s one parabola. And when we’ve seen people, for example, when they go on rides on NASA’s “Vomit Comet”… What we’ve seen from those types of parabolic flights is that people – if they get sick – its parabola six, seven, eight. It’s a delayed effect, really.

So you take SpaceX its one simple arc, it's not a sine wave like the vomit comet. You aren't going to throw up just from being weightless once in a simple flight.

One parabola with 15 - 20 min zero g. <-> 8 parabolas 45 s each = 6 min. I'm not convinced one long parabola is easier.

 

[jkn]

I have a seperate question. The original post by OP said that the BFR would experience up to 5g’s.

Is it group consensus that this is just plain wrong? That SpaceX will fly a profile that will never exceed 2g’s? Didn’t Elon say in the AMA that takeoff and landing will be 1.3 g’s?

At takeoff trust of a rocket is usually low (1.3 g's). While propellant is used, acceleration increases close to 3 g. 2. stage starts with < 1 g and increases to 3 g's. Faster acceleration is less propellant is used, but more (or larger) engines are needed. It is not possible to change this much.

5 g's with aerobrake only is easy. It is more difficult to keep it at 3 g's. Density of atmosphere doubles every 5 km down (roughly). So to deaccelerate 2.5 g's instead of 5 g rocket needs to be 5 km higher. Aerodynamic lift is needed for that.