Author Topic: SpaceX Falcon 9 : X-37B OTV-5 : September 7, 2017 : DISCUSSION  (Read 223456 times)

Online OneSpeed

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #420 on: 09/25/2017 12:34 pm »
LEO inclination changes can be done at any point in the orbit. It is only for GTO elliptical orbits where you really have to do it over the equator, otherwise your apogee is not going to be over the equator.

Again using launch from the Cape to equatorial LEO as an example (28° plane change requirement), by changing 28° at an orbital node (over the equator), an equatorial orbit is achieved directly (diagram 1). This is what I modelled for Comga.

If the burn was instead performed at maximum declination (28° latitude), the orbital plane would have been tipped sideways by 28° (diagram 2). The resultant orbit would have an inclination of 38°. If I had been trying to achieve equatorial orbit, any burn at maximum declination would have increased inclination, and been counter-productive. If I had been trying to increase inclination, then I would have obtained only a 10° change in declination for a 28° plane change.

Lastly, if I had been trying to increase inclination, and the burn had been performed at the equator, the resultant orbit would have a 56° inclination, nearly 3 x better (diagram 3). In short, yes you can change plane at any point in a low earth orbit, but changing plane is not the same as changing inclination, unless you do so at the equator.

Offline envy887

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #421 on: 09/25/2017 12:55 pm »
LEO inclination changes can be done at any point in the orbit. It is only for GTO elliptical orbits where you really have to do it over the equator, otherwise your apogee is not going to be over the equator.

Again using launch from the Cape to equatorial LEO as an example (28° plane change requirement), by changing 28° at an orbital node (over the equator), an equatorial orbit is achieved directly (diagram 1). This is what I modelled for Comga.

If the burn was instead performed at maximum declination (28° latitude), the orbital plane would have been tipped sideways by 28° (diagram 2). The resultant orbit would have an inclination of 38°. If I had been trying to achieve equatorial orbit, any burn at maximum declination would have increased inclination, and been counter-productive. If I had been trying to increase inclination, then I would have obtained only a 10° change in declination for a 28° plane change.

Lastly, if I had been trying to increase inclination, and the burn had been performed at the equator, the resultant orbit would have a 56° inclination, nearly 3 x better (diagram 3). In short, yes you can change plane at any point in a low earth orbit, but changing plane is not the same as changing inclination, unless you do so at the equator.

More concisely: you have to intersect a plane in order to burn into that plane, and you can only intersect the equatorial plane over the equator.

However, every non-SSO orbit intersects every SSO plane once per orbit: as long as you launch at the right time of day, you don't have to wait to cross the equator to burn into a specified SSO.

I'm not sure why X-37B would go to an equatorial orbit; yes, it good for hiding from amateur observers, but it's also terrible for looking at anything on the ground which is about the only reason to hide from amateur observers. A SSO orbit far from the terminator is also well hidden and much more useful.

Online OneSpeed

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #422 on: 09/25/2017 01:33 pm »
I'm not sure why X-37B would go to an equatorial orbit;

I'm not suggesting it would, I was just trying to show why it is advantageous to perform plane change at the equator.

However, every non-SSO orbit intersects every SSO plane once per orbit: as long as you launch at the right time of day, you don't have to wait to cross the equator to burn into a specified SSO.

You don't, but the more extreme the latitude of the burn, the more expensive it is.

Offline kevin-rf

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #423 on: 09/25/2017 02:03 pm »
Could OTV-5 have been spotted, if it has its much fainter than expected.

http://www.satobs.org/seesat/Sep-2017/0115.html

Ted Molczan's followup gives some search TLE's but cautions it could also fit TecSar (08002A / 32476) which was last observed in the spring of 2016.
http://www.satobs.org/seesat/Sep-2017/0118.html 

So, if it is OTV-5 and it is fainter than expected, could this indicate a deployable test of optical stealth technology. Something along the lines of Teledyne's famous patent? https://www.google.com/patents/US5345238
« Last Edit: 09/25/2017 03:16 pm by kevin-rf »
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Offline hkultala

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #424 on: 09/25/2017 02:04 pm »
I'm not sure why X-37B would go to an equatorial orbit;

I'm not suggesting it would, I was just trying to show why it is advantageous to perform plane change at the equator.

It is not advantageous to perform plane change at the equator.

it is very unadvantageous to perform plane change at the equator, but it is necessary when the target inclination is zero.

However, every non-SSO orbit intersects every SSO plane once per orbit: as long as you launch at the right time of day, you don't have to wait to cross the equator to burn into a specified SSO.

You don't, but the more extreme the latitude of the burn, the more expensive it is.

No, it's not. The higher velocity you perform the burn, the more expensive it is.

Changing the inclination early during the launch is cheap.
First going to orbit speed to wrong inclination and then changing inclination is very expensive.


Offline envy887

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #425 on: 09/25/2017 02:53 pm »
I'm not sure why X-37B would go to an equatorial orbit;

I'm not suggesting it would, I was just trying to show why it is advantageous to perform plane change at the equator.

It is not advantageous to perform plane change at the equator.

it is very unadvantageous to perform plane change at the equator, but it is necessary when the target inclination is zero.

For the specific case of going from a circular 28 degree LEO to a circular SSO at same altitude, this is incorrect.

It may help to visualize the various planes, but it comes down to this: the angle between a 28 degree orbit and SSO is greatest at highest latitude. When crossing the equator, there is a velocity component in the direction of the SSO, while at highest latitude the orbits are very nearly perpendicular.

However, is is still FAR cheaper to do the change while suborbital instead of waiting to cross the equator.

Offline Star One

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #426 on: 09/25/2017 05:01 pm »
Could OTV-5 have been spotted, if it has its much fainter than expected.

http://www.satobs.org/seesat/Sep-2017/0115.html

Ted Molczan's followup gives some search TLE's but cautions it could also fit TecSar (08002A / 32476) which was last observed in the spring of 2016.
http://www.satobs.org/seesat/Sep-2017/0118.html 

So, if it is OTV-5 and it is fainter than expected, could this indicate a deployable test of optical stealth technology. Something along the lines of Teledyne's famous patent? https://www.google.com/patents/US5345238

Here’s a further follow up on the matter.

http://www.satobs.org/seesat/Sep-2017/0120.html

http://www.satobs.org/seesat/Sep-2017/0121.html

And this.

http://www.satobs.org/seesat/Sep-2017/0123.html
« Last Edit: 09/25/2017 05:03 pm by Star One »

Offline kevin-rf

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #427 on: 09/25/2017 05:49 pm »
Here’s a further follow up on the matter.

http://www.satobs.org/seesat/Sep-2017/0120.html

http://www.satobs.org/seesat/Sep-2017/0121.html

And this.

http://www.satobs.org/seesat/Sep-2017/0123.html

As the thread progresses, it seems they are more and more convinced the sighting is TecSar and not OTV-5.
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Offline Star One

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #428 on: 09/25/2017 05:50 pm »
Here’s a further follow up on the matter.

http://www.satobs.org/seesat/Sep-2017/0120.html

http://www.satobs.org/seesat/Sep-2017/0121.html

And this.

http://www.satobs.org/seesat/Sep-2017/0123.html

As the thread progresses, it seems they are more and more convinced the sighting is TecSar and not OTV-5.

That’s certainly how I read it.

Offline Comga

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #429 on: 09/25/2017 06:56 pm »
For the specific case of going from a circular 28 degree LEO to a circular SSO at same altitude, this is incorrect.

It may help to visualize the various planes, but it comes down to this: the angle between a 28 degree orbit and SSO is greatest at highest latitude. When crossing the equator, there is a velocity component in the direction of the SSO, while at highest latitude the orbits are very nearly perpendicular.

However, is is still FAR cheaper to do the change while suborbital instead of waiting to cross the equator.

Pardon me
This was in answer to the question of whether NRO could have put OTV-5 into an orbit hard to track visually.
The hardest by that criterion could be a noon/midnight sun synchronous orbit.
I used the CCAFS to zero inclination calculation as a ROM on payload capacity of an F9 to that orbit. knowing that it was not a very good way to estimate it.  I did that because it's not a serious question, so not worth troubling our very capable modelers for a precise answer.

Thanks to all for the good insights into the orbital issues, and looking forward to if and when OTV-5 is positively identified.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Jim

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #430 on: 09/25/2017 08:14 pm »
My money is on the 2nd stage substantially changed the target inclination from the booster trajectory.
And X-37B has radar absorbing material, making it nearly impossible to detect it (helped by the sheer distance from the ground it flies at).
Its a secret space plane for a reason.

An basis for the claims about the radar-absorbing materials?

No reliable source seems to claim so.

Any reliable sources would be under threat of jail time if they said anything. Stealth is nothing new. Not putting some stealth on a space plane would be incompetence in my view.

wrong.

a.  It is a spaceplane for landing.  Its shape has nothing to do with it use on orbit
b.  This very shape is not stealthy
c.  X-37 can only carry 500lbs, that does not mix with stealth

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #431 on: 09/25/2017 08:15 pm »
So do you think the stealth coating is overtop or under the various thermal protection materials?
Perhaps on top, and burns up during re-entry and reapplied before each mission.
X-37B has a pretty cozy ride up, only gets cooked on the way down.
Pure speculation of course. But would make sense.

No, it makes no sense.  There is no such thing as a spray on stealth coating
« Last Edit: 09/25/2017 08:16 pm by Jim »

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #432 on: 09/25/2017 08:18 pm »

Inclination change is relatively cheap when it's done early enough (immediately after staging of rocket with low-impulse 1st stage). It's very expensive when it's done late

That is not a inclination "change" before it is in orbit, that is a dog leg
« Last Edit: 09/25/2017 08:28 pm by Jim »

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #433 on: 09/25/2017 08:27 pm »
In short, yes you can change plane at any point in a low earth orbit, but changing plane is not the same as changing inclination, unless you do so at the equator.

Wrong

What is meant by a dog leg.  It is during ascent before the vehicle is orbital.   The vehicle flies out at a certain azimuth and then steers to another one which changes the inclination.  The only limitation (other than propellant) is that the vehicle can not go to a lower inclination than the latitude it is at during the maneuver.


Also, inclination change does not have to be at the equator.  That is just the most efficient place for the maneuver,.  other locations are not as efficient and are subject to the above limitation.

Offline old_sellsword

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #434 on: 09/25/2017 08:33 pm »
In short, yes you can change plane at any point in a low earth orbit, but changing plane is not the same as changing inclination, unless you do so at the equator.

Wrong

What is meant by a dog leg.  It is during ascent before the vehicle is orbital.   The vehicle flies out at a certain azimuth and then steers to another one which changes the inclination.  The only limitation (other than propellant) is that the vehicle can not go to a lower inclination than the latitude it is at during the maneuver.


Also, inclination change does not have to be at the equator.  That is just the most efficient place for the maneuver,.  other locations are not as efficient and are subject to the above limitation.

Jim, does this maneuver require yaw (RAAN) steering? I believe you’ve stated before that Falcon 9 doesn’t have that capability.

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #435 on: 09/25/2017 08:42 pm »
RE: "observability" from the ground and "stealth"

If the USAF is making an effort to make the X-37B low-observable, what can be done without using any advanced materials or techniques (stealth)?

Does the X-37 have to orient itself in a similar way to Shuttle while in orbit?

IIRC, Shuttle on-orbit in independent flight, was most often oriented with the payload bay facing Earth.  The more reflective whlte blanketed/tiled surfaces faced the ground observers, while the black belly tiles faced outer space.

Thus, Shuttle was one of the brightest satellites in LEO.

What if the X-37 is orbiting with the black underside tiles facing Earth?  That would make its observed magnitude fainter--a lower albedo.

Or, what if the attitude is tail facing Earth?  It's a smaller surface area, less area to reflect sunlight.

An example: if the reflectivity is reduced to approximately 16% of the "normal" brightness, the apparent magnitude is reduced by 2.  A second magnitude satellite becomes a fourth magnitude satellite.

Nothing fancy, just basic physics and astronomy.

Just a thought--and certainly not a claim to be "the answer."

Math EDIT
« Last Edit: 09/25/2017 08:52 pm by zubenelgenubi »
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Offline meberbs

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #436 on: 09/25/2017 08:51 pm »
So do you think the stealth coating is overtop or under the various thermal protection materials?
Perhaps on top, and burns up during re-entry and reapplied before each mission.
X-37B has a pretty cozy ride up, only gets cooked on the way down.
Pure speculation of course. But would make sense.

No, it makes no sense.  There is no such thing as a spray on stealth coating
F-35 paint is classified, guess why.
http://www.businessinsider.com/where-f-35-gets-classified-features-2015-5

Offline Jirka Dlouhy

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #437 on: 09/25/2017 09:42 pm »
Is any information about Cubesats in this flight?

Online whitelancer64

So do you think the stealth coating is overtop or under the various thermal protection materials?
Perhaps on top, and burns up during re-entry and reapplied before each mission.
X-37B has a pretty cozy ride up, only gets cooked on the way down.
Pure speculation of course. But would make sense.

No, it makes no sense.  There is no such thing as a spray on stealth coating
F-35 paint is classified, guess why.
http://www.businessinsider.com/where-f-35-gets-classified-features-2015-5

Because it absorbs radar. Of course, we aren't talking about radar observations here, but optical.
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Offline meberbs

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Re: SpaceX Falcon 9 : X-37B OTV-5 : September 2017 : DISCUSSION
« Reply #439 on: 09/25/2017 10:27 pm »
So do you think the stealth coating is overtop or under the various thermal protection materials?
Perhaps on top, and burns up during re-entry and reapplied before each mission.
X-37B has a pretty cozy ride up, only gets cooked on the way down.
Pure speculation of course. But would make sense.

No, it makes no sense.  There is no such thing as a spray on stealth coating
F-35 paint is classified, guess why.
http://www.businessinsider.com/where-f-35-gets-classified-features-2015-5

Because it absorbs radar. Of course, we aren't talking about radar observations here, but optical.
That quote tree is based on discussion of radar stealth.

Spray on optical stealth for space is pretty obvious (black paint), so I am pretty sure that isn't what Jim was referring to either.

Last on the list of observation methods would be IR, and control of IR with paint is a consideration in spacecraft thermal design anyway. The RF paint is the obscure one that I wouldn't have guessed existed either if I hadn't heard about it before.

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