Discussion of Starship's Test Launch - Orbital versus Sub-Orbital

[bxr140]

Thread title correction: Sub-orbital.

Getting into a stable orbit is much more than just ~equivalent ballistic energy, and given the amount of rigor the regulars here put on other entities those folks are sure they’re sure to give you a hard time for the obvious over-representation.

 

[Grendal]

Thread title correction: Sub-orbital.

Getting into a stable orbit is much more than just ~equivalent ballistic energy, and given the amount of rigor the regulars here put on other entities those folks are sure they’re sure to give you a hard time for the obvious over-representation.

I'm not sure what speed they intend to reach. Everyone else is naming it the "orbital launch test," so I'm giving it that heading as well. I expect the "test" gives it the leeway for a close to orbital speed. But technically you are likely correct.

 

[Cosmacelf]

Thread title correction: Sub-orbital.

Getting into a stable orbit is much more than just ~equivalent ballistic energy, and given the amount of rigor the regulars here put on other entities those folks are sure they’re sure to give you a hard time for the obvious over-representation.

Apparently the trajectory it will attain has about the same energy as a full orbital trajectory, so close enough.

 

[ecarfan]

Apparently the trajectory it will attain has about the same energy as a full orbital trajectory, so close enough.

Agreed. I posted this in the Starship General Development thread.

Just in case the issue of whether or not the upcoming Starship launch profile is an “orbital” or “suborbital” trajectory, this diagram posted by @theradicalmoderate on ars technica provides an explanation.

View attachment 924125

 

[ggr]

Thread title correction: Sub-orbital.

Getting into a stable orbit is much more than just ~equivalent ballistic energy, and given the amount of rigor the regulars here put on other entities those folks are sure they’re sure to give you a hard time for the obvious over-representation.

If you can get more than half way around the earth, you could have entered orbit, by using delta-v to circularize rather than allowing the vehicle to re-enter. (At least that's what my orbital mechanics amateur intuition tells me.)

 

[bxr140]

If you can get more than half way around the earth, you could have entered orbit, by using delta-v to circularize rather than allowing the vehicle to re-enter. (At least that's what my orbital mechanics amateur intuition tells me.)

As noted above, getting into a stable orbit is more than just energy. And more difficult than just hucking something up real high and waiting for it to come back. If it was simply a matter of energy SX would just go orbital, because obviously there's no energy capabaility/capacity limitation.

Anyway, here's hoping they have a successful sub-orbital flight and that they can go for actual orbital sometime in the near future.

 

[Electroman]

Suborbital sounds so BOish !!

 

[scaesare]

Thread title correction: Sub-orbital.

Getting into a stable orbit is much more than just ~equivalent ballistic energy, and given the amount of rigor the regulars here put on other entities those folks are sure they’re sure to give you a hard time for the obvious over-representation.

I agree that if you aren't going orbital., well then it's not truly an orbital test.

That having been said, what is the "much more" that's involved other than ballistic energy? My assumption is that it's control? If you are able to control the rocket to put it on a specific trajectory hitting the perigee/apogee needed to splash down in a specific location, then haven't you also demonstrated control?

What significant other effort is there besides energy and control that's needed?

 

[mongo]

As noted above, getting into a stable orbit is more than just energy. And more difficult than just hucking something up real high and waiting for it to come back. If it was simply a matter of energy SX would just go orbital, because obviously there's no energy capabaility/capacity limitation.

Anyway, here's hoping they have a successful sub-orbital flight and that they can go for actual orbital sometime in the near future.

Sure, it's more than just energy, you need energy in the correct direction. If Starship lands off Hawaii, it had sufficient quantities of both. The deltaV difference at apogee between 300x300 and 100x300 is about 60m/s out of 7700m/s or 1%. 50x300 is 75 m/s, still under 1%. Even factoring kinetic energy as mass times velocity squared, it's still only a 2% difference.
Heck, 0 x 300 is only 90m/s difference (1.2%) one fifth of the Earth's velocity at the Equator.

Orbital speed: Check
Orbital apogee: Check
Orbital perigee: Not as long as Earth has an atmosphere

Then why not "just go orbital"?

Creating a stable orbit only needs one burn total (for that stage). However, reentry from a stable orbit requires a second burn. (ok, if your engines really throttle, you could do everything with one). They likely want to reduce the risk of Starship staying in orbit uncontrolled since it's specifically build not built to burn up on reentry.

I could be wrong and they do plan a retro burn, in which case it's definitely orbital. However, the old timeline/ flight path doesn't call that out.

 

[bxr140]

What significant other effort is there besides energy and control that's needed?

Clearly enough that SX decided this first flight into space be sub-orbital and not orbital.

Suborbital sounds so BOish !!

Which is really the main point here: Ya'll are too easy to troll.

 

[mongo]

Clearly enough that SX decided this first flight into space be sub-orbital and not orbital.

Legally, if the orbit, in a vaccum, clears the terrain, it's not a sub-orbital flight.

14 CFR § 401.5 - Definitions.

Suborbital rocket means a vehicle, rocket-propelled in whole or in part, intended for flight on a suborbital trajectory, and the thrust of which is greater than its lift for the majority of the rocket-powered portion of its ascent.

Suborbital trajectory means the intentional flight path of a launch vehicle, reentry vehicle, or any portion thereof, whose vacuum instantaneous impact point does not leave the surface of the Earth.

Instantaneous impact point means a predicted impact point, following thrust termination of a vehicle.

 

[scaesare]

Clearly enough that SX decided this first flight into space be sub-orbital and not orbital.

There's been discussion here about that... it's much more likely that the issue is deliberately giving it a trajectory where it can simply fall out of the sky over a non-populated area should something go wrong, yet at the same time perform a sufficient flight that proves out enough thrust for going orbital, and testing the flight control surfaces, gimbal system, etc... Also not risking the tower and pad for a chopsticks recovery.

None of that would seem to meet the threshold of needing to do "much more" to acheive orbit as you asserted. What am I missing that is significant to get to orbit they aren't doing/proving out? Isn't it just matter of a slightly different thrust vector during ascent?

 

[bxr140]

There's been discussion here about that... it's much more likely that the issue is deliberately giving it a trajectory where it can simply fall out of the sky over a non-populated area should something go wrong, yet at the same time perform a sufficient flight that proves out enough thrust for going orbital, and testing the flight control surfaces, gimbal system, etc... Also not risking the tower and pad for a chopsticks recovery.

Lol, that's my point. Despite all the talk here about how easy it would be to just go into a stable orbit and how incremental/eqivalent-ey this trajectory is to actually orbiting, the risk is just too high for SX to attempt doing that on this launch.

Not to be missed, the corollary point is that it's fun to rattle the cage when the home team fans are the ones making shoulda-coulda-woulda excuses.

Anyway, again, good luck on the sub-orbital flight, SX!

 

[scaesare]

Lol, that's my point. Despite all the talk here about how easy it would be to just go into a stable orbit and how incremental/eqivalent-ey this trajectory is to actually orbiting, the risk is just too high for SX to attempt doing that on this launch.

Not to be missed, the corollary point is that it's fun to rattle the cage when the home team fans are the ones making shoulda-coulda-woulda excuses.

Anyway, again, good luck on the sub-orbital flight, SX!

But that wasn't the point you made. You said:

Getting into a stable orbit is much more than just ~equivalent ballistic energy...

And it's been pointed out by @mongo, myself, and others that the other significant item is control. And that is has to be working correctly for the flight path they intend to demonstrate. They aren't just "hucking something up real high and waiting for it to come back."... this isn't a hop-test.

And the follow on assertion you made was (regarding the effort needed to do an orbital test):

Clearly enough that SX decided this first flight into space be sub-orbital and not orbital.

But as has also been pointed out, it's not that any more effort is needed, it's that they don't want to overfly populated areas or risk the pad.

So, please, just tell us. What effort is involved that's "much more" than what this test will do?

 

[mongo]

Which is really the main point here: Ya'll are too easy to troll.

The main point here in this thread is discussing the test flight.

Not to be missed, the corollary point is that it's fun to rattle the cage when the home team fans are the ones making shoulda-coulda-woulda excuses.

So we should just ignore you then since you are writing only to be purposely annoying and disingenuous?

Some of us actually care about facts, feel free to present some. For instance:
Any authorative source you have to show Starship is not doing a deorbit burn to support your claim of sub-orbital.
An authoritative source that overrides the US Federal definition of "sub-orbital" to support your definition.
At a minimum, a (your?) definition for the unboosted time in orbit required to be considered "stable".

 

[Cosmacelf]

Ignore the trolls guys, and BXR140, this obviously isn't the forum for poking the bears, please drop it lest this thread be deleted and a new one needed to be created (which isn't a bad idea at this point).

 

[bxr140]

Some of us actually care about facts, feel free to present some.

First, I summarily reject your selective application of "just the facts ma'am" in this thread simply because you don't like what I'm saying. Nobody here gets on the 'just the facts' rant train when someone makes crazy statements about SX or when someone makes some disparaging and incorrect statement about a competitor.

Moving on, let's all just imagine for a second if this were NG or Vulcan or SLS making this flight and calling it orbital.

Circling back to the facts, folks in this thread and elsewhere have intimated that this mission "should count" as orbital because the energy to get into a stable (= periodic) orbit is similar to the energy of the nominal mission. The fact is that SX is NOT electing to do this because the difficulty (= risk) is too high. Please provide some factual evidence to the contrary if you disagree.

Regarding the mission profile, it's purposely a low-risk, free-return option. That they are [presumably] planning some burns doesn't change the fact that they're planning on a worst case, uncontrolled vehicle.

Finally, shades of Shepard/Glenn come to mind here.

BXR140, this obviously isn't the forum for poking the bears, please drop it lest this thread be deleted and a new one needed to be created (which isn't a bad idea at this point).

Nope. Ya'll don't get to reject something simply because you don't like what's being said.

(I appreciate there's some hurt feelings on how it's being said. )

 

[scaesare]

difficulty (!= risk)

Fixed that for you so it's a fact.