Author Topic: Reviving manned Dream Chaser?  (Read 9704 times)

Online envy887

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Re: Reviving manned Dream Chaser?
« Reply #40 on: 08/13/2018 02:17 PM »
The debate wasn't about shuttle system as a whole but wing vehicle vs capsule on reentry. The shuttle vehicle didn't fail because of its design. The complete launch system that shuttle used to get to space did fail twice.

Agreed the orbiter part of the system was very reliable so long as there were no anomalies during launch.
The aircraft style landing mode is so far in practice has been the safest way to bring back a vehicle.

You need to add the qualifier "no anomalies during launch", but that's not really a fair way of judging it since the anomaly on launch was something that happened only because it was a winged design.

Winged designs cause all sorts of other design decisions.  With Columbia, one of the design decisions caused by going with a winged design caused the loss of Columbia.  It's not fair to absolve the winged design of that failure because it's a direct result of the winged design.  A capsule would not have failed this way.

Winged designs have a worse rate of killing people than capsules.  Maybe future winged designs will be safer, but that's the nature of looking at historical results.  The historical results, so far, say that winged designs are less safe.

Other winged designs in the future may not have the same failures that have been seen in the past.  But the fundamental underlying cause is still there: winged designs are more complex, and that added complexity causes trade-offs throughout the system, trade-offs that can lead to loss of the crew.

I dont  agree with that

the shuttle "system" (a more precise word than spacecraft I admit) failed because 1) the design had some inherent defects 2) NASA insisted on flying the system with those defects, 3) they insisted on flying the system in an environment where the defect(s) got worse and 4) ignored a known event and did nothing to verify that the vehicle was safe

A capsule, side mounted on the ET/SRB stack would have concievably had exactly the same problems.  without an escape system the Challenger accident would have still been fatal...and while the foam coming off the vehicle would not have impacted a side mounted capsules "heatshield" it would have impacted the vehicle..and "could" have been catastrophic as well...

you might have a point if say an orbiter had been lost (as a lot of people thought Columbia initially was) by the difficulty of going from stalled to flying or more correctly from "controlled brick" to lifting body.

but as best I know that never was even close to being an issue

the fly by wire system on the shuttle was amazing period much less for its then novelty. on Columbia it held control of the vehicle until control was simply impossible

A capsule on Shuttle-C would have been much safer.

Note that the foam strike was far downstream of the crew cabin on Columbia. The only foam upstream of the crew cabin (which is where a capsule would have been), was the acreage SOFI which did not have shedding issues. The bipod ramps had the shedding issues, but they were downstream of where a side-mount capsule would have been.

And Challenger survived the stack breakup but disintegrated under aeroloads when it exceeded its allowable angle of attack at that speed. A capsule likely wouldn't have had any AoA restrictions at those speeds, and likely would have emerged from the conflagration basically intact and able to pop its chutes, even if it didn't have an abort motor.

I don't know if DreamChaser has any AoA restrictions, but if it does the abort motor better be able to positively control AoA during an anomaly or it could break up like Challenger. Other than that, it's probably about as safe as a capsule.

Offline JAFO

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Re: Reviving manned Dream Chaser?
« Reply #41 on: 08/13/2018 02:44 PM »
“Flaming meteors of solid propellant” I think was the term used to argue against a capsule on a vehicle using SRBs in case of an abort where the SRBs would have been unzipped, potentially resulting in parachute failure if one struck a chute on the way down.


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Offline TripleSeven

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Re: Reviving manned Dream Chaser?
« Reply #42 on: 08/13/2018 03:16 PM »
The debate wasn't about shuttle system as a whole but wing vehicle vs capsule on reentry. The shuttle vehicle didn't fail because of its design. The complete launch system that shuttle used to get to space did fail twice.

Agreed the orbiter part of the system was very reliable so long as there were no anomalies during launch.
The aircraft style landing mode is so far in practice has been the safest way to bring back a vehicle.

You need to add the qualifier "no anomalies during launch", but that's not really a fair way of judging it since the anomaly on launch was something that happened only because it was a winged design.

Winged designs cause all sorts of other design decisions.  With Columbia, one of the design decisions caused by going with a winged design caused the loss of Columbia.  It's not fair to absolve the winged design of that failure because it's a direct result of the winged design.  A capsule would not have failed this way.

Winged designs have a worse rate of killing people than capsules.  Maybe future winged designs will be safer, but that's the nature of looking at historical results.  The historical results, so far, say that winged designs are less safe.

Other winged designs in the future may not have the same failures that have been seen in the past.  But the fundamental underlying cause is still there: winged designs are more complex, and that added complexity causes trade-offs throughout the system, trade-offs that can lead to loss of the crew.

I dont  agree with that

the shuttle "system" (a more precise word than spacecraft I admit) failed because 1) the design had some inherent defects 2) NASA insisted on flying the system with those defects, 3) they insisted on flying the system in an environment where the defect(s) got worse and 4) ignored a known event and did nothing to verify that the vehicle was safe

A capsule, side mounted on the ET/SRB stack would have concievably had exactly the same problems.  without an escape system the Challenger accident would have still been fatal...and while the foam coming off the vehicle would not have impacted a side mounted capsules "heatshield" it would have impacted the vehicle..and "could" have been catastrophic as well...

you might have a point if say an orbiter had been lost (as a lot of people thought Columbia initially was) by the difficulty of going from stalled to flying or more correctly from "controlled brick" to lifting body.

but as best I know that never was even close to being an issue

the fly by wire system on the shuttle was amazing period much less for its then novelty. on Columbia it held control of the vehicle until control was simply impossible

A capsule on Shuttle-C would have been much safer.

Note that the foam strike was far downstream of the crew cabin on Columbia. The only foam upstream of the crew cabin (which is where a capsule would have been), was the acreage SOFI which did not have shedding issues. The bipod ramps had the shedding issues, but they were downstream of where a side-mount capsule would have been.

And Challenger survived the stack breakup but disintegrated under aeroloads when it exceeded its allowable angle of attack at that speed. A capsule likely wouldn't have had any AoA restrictions at those speeds, and likely would have emerged from the conflagration basically intact and able to pop its chutes, even if it didn't have an abort motor.

I don't know if DreamChaser has any AoA restrictions, but if it does the abort motor better be able to positively control AoA during an anomaly or it could break up like Challenger. Other than that, it's probably about as safe as a capsule.

its speculation as to what the airflow dynamics would have been with a crewed capsule on top of some "propulsion" stage in terms of the foam, as it was, what was the phrase,  'being liberated" from the tanks.  I agree that the odds would be "better" with a capsule.

I dont agree with your comment on Challenger at all.  any capsule on a sidemounted stick would have had some kind of propulsion system which would have been destroyed in the "seconds" that the external tank exploded.  and that would have 1) done some damage to the capsule, 2) induced massive G forces on the capsule and even 3) had it somehow survived its unclear that it would have not been penetrated by debris or be in a dynamic state that was recoverable to deploy chutes

Its been a really long time (like decades) since I looked at the dynamics of the vehicle destruction but I doubt severely they were aerodynamic loads...and expect more likely they were overpressure damage done as the tank "exploded".  the over pressure would have been even more catastrophic on a relatively weak (compared with the shuttle orbiter) expendable stage. 

the only real serious "part" of the shuttle orbiter that emerges from the conflagration ...was the crew compartment (pressure vessel) which was venting quickly to ambient pressure.

I suspect that a crew capsule would have had nearly the same "disassembly" ie the pressure vessel would remain intact but the rest of it would "shed"

this is all speculation of course...but I dont know that I would embrace "much safer" in terms of a Capsule on a Shuttle C stack.

its unclear to me that even an LAS would have worked "in time" unless it activated based on the flight parameters that were occurring because of the blowby ie engines pivoting to deal with thrust issues.
« Last Edit: 08/13/2018 03:19 PM by TripleSeven »

Online envy887

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Re: Reviving manned Dream Chaser?
« Reply #43 on: 08/13/2018 07:10 PM »
The debate wasn't about shuttle system as a whole but wing vehicle vs capsule on reentry. The shuttle vehicle didn't fail because of its design. The complete launch system that shuttle used to get to space did fail twice.

Agreed the orbiter part of the system was very reliable so long as there were no anomalies during launch.
The aircraft style landing mode is so far in practice has been the safest way to bring back a vehicle.

You need to add the qualifier "no anomalies during launch", but that's not really a fair way of judging it since the anomaly on launch was something that happened only because it was a winged design.

Winged designs cause all sorts of other design decisions.  With Columbia, one of the design decisions caused by going with a winged design caused the loss of Columbia.  It's not fair to absolve the winged design of that failure because it's a direct result of the winged design.  A capsule would not have failed this way.

Winged designs have a worse rate of killing people than capsules.  Maybe future winged designs will be safer, but that's the nature of looking at historical results.  The historical results, so far, say that winged designs are less safe.

Other winged designs in the future may not have the same failures that have been seen in the past.  But the fundamental underlying cause is still there: winged designs are more complex, and that added complexity causes trade-offs throughout the system, trade-offs that can lead to loss of the crew.

I dont  agree with that

the shuttle "system" (a more precise word than spacecraft I admit) failed because 1) the design had some inherent defects 2) NASA insisted on flying the system with those defects, 3) they insisted on flying the system in an environment where the defect(s) got worse and 4) ignored a known event and did nothing to verify that the vehicle was safe

A capsule, side mounted on the ET/SRB stack would have concievably had exactly the same problems.  without an escape system the Challenger accident would have still been fatal...and while the foam coming off the vehicle would not have impacted a side mounted capsules "heatshield" it would have impacted the vehicle..and "could" have been catastrophic as well...

you might have a point if say an orbiter had been lost (as a lot of people thought Columbia initially was) by the difficulty of going from stalled to flying or more correctly from "controlled brick" to lifting body.

but as best I know that never was even close to being an issue

the fly by wire system on the shuttle was amazing period much less for its then novelty. on Columbia it held control of the vehicle until control was simply impossible

A capsule on Shuttle-C would have been much safer.

Note that the foam strike was far downstream of the crew cabin on Columbia. The only foam upstream of the crew cabin (which is where a capsule would have been), was the acreage SOFI which did not have shedding issues. The bipod ramps had the shedding issues, but they were downstream of where a side-mount capsule would have been.

And Challenger survived the stack breakup but disintegrated under aeroloads when it exceeded its allowable angle of attack at that speed. A capsule likely wouldn't have had any AoA restrictions at those speeds, and likely would have emerged from the conflagration basically intact and able to pop its chutes, even if it didn't have an abort motor.

I don't know if DreamChaser has any AoA restrictions, but if it does the abort motor better be able to positively control AoA during an anomaly or it could break up like Challenger. Other than that, it's probably about as safe as a capsule.

its speculation as to what the airflow dynamics would have been with a crewed capsule on top of some "propulsion" stage in terms of the foam, as it was, what was the phrase,  'being liberated" from the tanks.  I agree that the odds would be "better" with a capsule.

I dont agree with your comment on Challenger at all.  any capsule on a sidemounted stick would have had some kind of propulsion system which would have been destroyed in the "seconds" that the external tank exploded.  and that would have 1) done some damage to the capsule, 2) induced massive G forces on the capsule and even 3) had it somehow survived its unclear that it would have not been penetrated by debris or be in a dynamic state that was recoverable to deploy chutes

Its been a really long time (like decades) since I looked at the dynamics of the vehicle destruction but I doubt severely they were aerodynamic loads...and expect more likely they were overpressure damage done as the tank "exploded".  the over pressure would have been even more catastrophic on a relatively weak (compared with the shuttle orbiter) expendable stage. 

the only real serious "part" of the shuttle orbiter that emerges from the conflagration ...was the crew compartment (pressure vessel) which was venting quickly to ambient pressure.

I suspect that a crew capsule would have had nearly the same "disassembly" ie the pressure vessel would remain intact but the rest of it would "shed"

this is all speculation of course...but I dont know that I would embrace "much safer" in terms of a Capsule on a Shuttle C stack.

its unclear to me that even an LAS would have worked "in time" unless it activated based on the flight parameters that were occurring because of the blowby ie engines pivoting to deal with thrust issues.

From the Rogers Commission report:

Quote
All fractures and material failures examined on the Orbiter, with the exception of the main engines, were the result of overload forces, and they exhibited no evidence of internal burn damage or exposure to explosive forces. This indicated that the destruction of the Orbiter occurred predominantly from aerodynamic and inertial forces that exceeded design limits.

And also:

Quote
If a problem arose that required the Orbiter to get away from failing Solid Rocket Boosters, the separation would have to be performed extremely quickly. Time would be of the essence for two reasons. First, as 51-L demonstrated, if a problem develops in a Solid Rocket Booster, it can escalate very rapidly. Second, the ascent trajectory is carefully designed to control the aerodynamic loads on the vehicle; very small deviation from the normal path will produce excessive loads, so if the vehicle begins to diverge from its path there is very little time (seconds) before structural breakup will occur.

The normal separation sequence to free the Shuttle from the rest of the system takes 18 seconds, far too long to be of use during a firststage contingency. "Fast-separation" was formally established by Review Item Discrepancy 03.00.151, which stated the requirement to separate the Orbiter from the External Tank at any time. The sequence was referred to as fast-separation because delays required during normal separation were bypassed or drastically shortened in order to achieve separation in approximately three seconds. Some risk was accepted to obtain this contingency capability. Fast-separation was incorporated into the flight software, so that technically this capability does exist. Unfortunately, analysis has shown that, if it is attempted while the Solid Rocket Boosters are still thrusting, the Orbiter will "hang up" on its aft attach points and pitch violently, with probable loss of the Orbiter and crew. In summary, as long as the Solid Rocket Boosters are still thrusting, fast-separation does not provide a way to escape. It would be useful during first stage only if Solid Rocket Booster thrust could first be terminated.

Bold mine. Loss of pitch control at speed would result in rapid breakup of the Orbiter. This is an inherent issue with vehicles with slender aspect ratios, and much less of a problem with blunt capsules.

In fact, in the only example of a blunt capsule undergoing a stage overpressure event, it survived intact and kept transmitting telemetry all the way to the radio horizon:

Quote
... the first stage actually continued to power through the overpressure event on the second stage for several seconds following the mishap.  In addition, the Dragon spacecraft not only survived the second stage event, but also continued to communicate until the vehicle dropped below the horizon and out of range.

Dream Chaser has an abort motor that is presumably able to maintain attitude control throughout an abort. Also, its compact lifting body design likely allows much higher aerodynamic loading without structural failure compared to the longer, thinner Shuttle.

Offline TripleSeven

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Re: Reviving manned Dream Chaser?
« Reply #44 on: 08/13/2018 07:16 PM »
envy887




"All fractures and material failures examined on the Orbiter, with the exception of the main engines, were the result of overload forces, and they exhibited no evidence of internal burn damage or exposure to explosive forces. This indicated that the destruction of the Orbiter occurred predominantly from aerodynamic and inertial forces that exceeded design limits."

yeap in this case "aerodynamic and inertial forces" are  overpressure.  doubtless we have a different understanding of aerodynamic and inertial forces...I am good with mine :) its got me this far

as for Dream Chaser...who knows...but it would not have been capable of riding on the shuttle stack.  it would need well somewhere to put the SSME's that were required to get the entire stack into orbit :)


" Also, its compact lifting body design likely allows much higher aerodynamic loading without structural failure compared to the longer, thinner Shuttle."

maybe...maybe not

"In fact, in the only example of a blunt capsule undergoing a stage overpressure event, it survived intact and kept transmitting telemetry all the way to the radio horizon:"

not relevant as the capsule was no where in the "overpressure" event wave or as the rogers commission would put it the "aerodynamic and inertial forces" of the blast.

anyway I am off to bed...reserve tomorrow...its not a point worth going on with...  stay safe
« Last Edit: 08/13/2018 07:23 PM by TripleSeven »

Offline Lar

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Re: Reviving manned Dream Chaser?
« Reply #45 on: 08/14/2018 09:32 PM »
(mod) Let's not rehash both the shuttle tragedies in a thread that's not about shuttle. If you want to reference them, please make sure that your reference is the minimum necessary to make your DC point. Quoting long sections from reports probably is not a good approach.

Thanks.

Also, TripleSeven, learn how to use the quote function. That means quotes that look like this

anyway I am off to bed...reserve tomorrow...its not a point worth going on with...  stay safe

not like this

"anyway I am off to bed...reserve tomorrow...its not a point worth going on with...  stay safe"
« Last Edit: 08/14/2018 09:34 PM by Lar »
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Offline Rocket Science

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Re: Reviving manned Dream Chaser?
« Reply #46 on: 08/16/2018 01:41 PM »
With Mark sadly leaving SNC it leaves me wondering if this is the final nail in a crewed Dream Chaser; however I hope it isn't...
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Offline docmordrid

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Re: Reviving manned Dream Chaser?
« Reply #47 on: 08/17/2018 10:49 AM »
>
The main problem was not the wings, it was the side mounting. A capsule astride a Shuttle-C would have also been subject to debris strikes. This is not to say that wings or lifting bodies don't present problems, but they are resolvable.

The death rate aboard winged vehicles is higher simply because STS flew more people.

And because it was in position to be struck by debris.

I see two poor decisions in the years after Challenger,

1) continuing to haul heavy cargo in a crewed vehicle vs. launching them on an ELV, or today an RLV. Extra points for increasing the flight rate of those vehicles.

2) failing to develo a top mount crew vehicle to replace the Orbiter, especially HL-20 PLS.   
« Last Edit: 08/17/2018 10:50 AM by docmordrid »
DM

Offline Patchouli

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Re: Reviving manned Dream Chaser?
« Reply #48 on: 08/20/2018 05:10 PM »

Dream Chaser has an abort motor that is presumably able to maintain attitude control throughout an abort. Also, its compact lifting body design likely allows much higher aerodynamic loading without structural failure compared to the longer, thinner Shuttle.

In an early launch failure especially if the LV has solids DC or any other space plane type vehicle actually has advantage over a capsule in that it doesn't have to worry about having the flaming debris melt it's parachutes.
A TPS covered wing is a lot more resistant to flaming debris than a nylon parachute.
If chutes are still used for an emergency landing scenario it still has a slower drop rate along with more forward travel which gives it more time to wait out the debris cloud and get farther away from it.
« Last Edit: 08/20/2018 05:17 PM by Patchouli »

Offline jbenton

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Re: Reviving manned Dream Chaser?
« Reply #49 on: 09/09/2018 12:00 AM »
“Flaming meteors of solid propellant” I think was the term used to argue against a capsule on a vehicle using SRBs in case of an abort where the SRBs would have been unzipped, potentially resulting in parachute failure if one struck a chute on the way down.


I hate saying that, because I was a huge Direct fanboy.

I have often wondered about how Starliner and Orion get around that. It helps Starliner, at least, that monolithic solids are inherently safer than segmented ones.


Dream Chaser has an abort motor that is presumably able to maintain attitude control throughout an abort. Also, its compact lifting body design likely allows much higher aerodynamic loading without structural failure compared to the longer, thinner Shuttle.

In an early launch failure especially if the LV has solids DC or any other space plane type vehicle actually has advantage over a capsule in that it doesn't have to worry about having the flaming debris melt it's parachutes.
A TPS covered wing is a lot more resistant to flaming debris than a nylon parachute.
If chutes are still used for an emergency landing scenario it still has a slower drop rate along with more forward travel which gives it more time to wait out the debris cloud and get farther away from it.

 I thought the "flaming meteors of solid propellant" would be a risk for the spacecraft itself too, not just the parachutes. Therefore, I supposed that even DreamChaser would be at risk due to solids, but I suppose I was wrong.

Obviously the safety of a launch abort is important, but what about comfort. This is what an abort scenario looks like for the Dragon capsule:





There is some rotation between separation and chute deployment. It looks at least a little uncomfortable. If I'm not mistaken, launch aborts involving towers are even worse.

This had me wondering: what would the Dream Chaser launch abort profile look like? would it just be a simple parabolic arc (at least until the craft achieves aerodynamic stability and levels out) followed by a landing "across the pond" (or ditching in the ocean, if pad abort)?

Not trying to restart capsule v. spaceplane argument, just curious what that would look like.
« Last Edit: 09/09/2018 12:02 AM by jbenton »

Offline jbenton

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Re: Reviving manned Dream Chaser?
« Reply #50 on: 09/09/2018 12:01 AM »
Catdlr posted this on the Dream Chaser UPDATE thread:

SNC Dream Chaser Capabilities Overview - 2018
Sierra Nevada Corporation
Published on Aug 30, 2018

https://www.youtube.com/watch?v=AxjzHgrzhoc?t=001



Whether or not it's happening, SNC is still advertising crewed capability.

What excites me most is that there appears to be a square just behind the cockpit which could be a second docking hatch. This could be ideal for a Hubble servicing mission. (They could use this to dock with the Hubble, the abort motors are now free to provide orbit re-boost; also an airlock could be mounted in lieu of the aft docking-hatch) Although, it's probably only the crew ingress-egress hatch for use on the launch pad.

Offline jbenton

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Re: Reviving manned Dream Chaser?
« Reply #51 on: 09/09/2018 12:02 AM »
Just wondering, with the delays being encountered by Dragon 2 and Starliner, how much it would take for NASA to say "Let's revive this program as a third option."? I know SNC has been saying the Cargo Dream Chaser is about 85% compatible with the manned one, would NASA have to redo the bid?

I don't know if they'd ever consider the Dream Chaser as a third option for ISS missions, but the Hubble could use another servicing mission sometime next decade.

A somewhat recent post on the Hubble thread:

Somewhat older, but on checking the thread I couldn't see mention of it.
http://www.stsci.edu/hst/proposing/panel/Cycle25-HST-status.pdf

This is the status of Hubble as of June 2017.

Highlights:
Gyro life estimate is till 2023, with three gyros, and reduced operation on one gyro out to 2036. (if of course it remains working and funded, it gets rather less useful with less than three gyros).
40 PHds generated per year.
$100M budget.
6:1 more demand for telescope time than there is.

There seems to be some degradation of certain instruments that gets worse over time, but it seems likely that if a gyros does fail in 2023, the telescope would otherwise be mostly healthy and still doing science until then.

Something to bookmark for June, to look at changes.

Whenever there is chatter 'bout the "saving the Hubble", Dream Chaser comes up.
This is a post from the Dream Chaser DISCUSSION thread three years ago:

Found this article: http://spacenews.com/op-ed-a-not-so-final-servicing-mission/

from the article:
Quote
In December 2014, David L. Akin of the University of Maryland’s Space Systems Laboratory presented the results of his study of maintaining Hubble using the Crew Dragon or Sierra Nevada Corp.’s Dream Chaser commercial crew spaceplane.
Quote
Akin said he did not have enough details about the other winner of NASA’s commercial crew competition, Boeing’s CST-100, to evaluate it for a Hubble maintenance mission. It is not clear that the CST-100 would be able to carry the required cargo, although that might be launched on a separate flight. Akin concluded that the loser in NASA’s commercial crew competition, Sierra Nevada’s Dream Chaser mini-shuttle, would offer some advantages over Dragon.
emphasis mine.

Most of the article is about the Hubble and Dragon. This part is pretty deep into the article. Does anyone know where to find the text or a presentation of this study?

For the record, no one ever answered my question  ;)


In any case apparently there was a formal proposal to use the Dream Chaser to do exactly that back in 2017:

http://www.spaceflightinsider.com/missions/space-observatories/trump-space-advisors-considering-hubble-servicing-mission/
https://phys.org/news/2017-02-chaser-spacecraft-hubble-mission.html
http://www.parabolicarc.com/2017/02/14/dream-chaser-service-hubble-space-telescope/
https://www.universetoday.com/133429/dream-chaser-spacecraft-may-used-hubble-repair-mission/

Each of these is just reporting on the Wall Street Journal reporting on the proposal, choose your favorite.
The first one mentions that Dream Chaser lacks the robotic arm and considers that a problem as that is what Shuttle used to grapple Hubble (I wouldn't consider that much of a problem, because STS-125 added the Soft Capture Mechanism to allow vehicles other than Hubble to do the job) The lack of an arm does mean, though that the 'nauts would probably need to make use of a manned maneuverability unit.

The first article also makes mention of the expendable mission module, which could be used as an airlock. (though I'm not sure how it would fit on the launch configuration of a crewed Dream Chaser. There's also the added expense of having an expendable airlock)
« Last Edit: 09/12/2018 12:55 AM by jbenton »

Offline brickmack

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Re: Reviving manned Dream Chaser?
« Reply #52 on: 09/09/2018 04:22 PM »
What excites me most is that there appears to be a square just behind the cockpit which could be a second docking hatch. This could be ideal for a Hubble servicing mission. (They could use this to dock with the Hubble, the abort motors are now free to provide orbit re-boost; also an airlock could be mounted in lieu of the aft docking-hatch) Although, it's probably only the crew ingress-egress hatch for use on the launch pad.

The square behind the cockpit is the hatch for entry on the pad. No docking port there. The DC4Science slides show that this hatch can be opened in orbit for experiment deployment, but for a manned mission an airlock is probably best. The aft hatch (where the docking port is) can also be used with or without a dedicated airlock, and this is what most studies have assumed (probably because of the difficulty of translating across the top of DC, with no handrails and without damaging the TPS). There were a couple EVA tests performed in the NBL for aft-port egress and ingress on DC.

The first article also makes mention of the expendable mission module, which could be used as an airlock. (though I'm not sure how it would fit on the launch configuration of a crewed Dream Chaser. There's also the added expense of having an expendable airlock)

In SNC's servicing studies from years ago, the mission module would've basically just been a cylindrical airlock (radial hatch, unpressurized axial NDS port) extending like 2ish meters down from where the docking port normally is, and a smallish robotic arm and possibly some toolboxes/replacement parts would be radially mounted on the mission module. It was all sized to fit inside the launch vehicle adapter. Could also eliminate the airlock (or use an internal airlock) and just have an arm mounted on the aft end
« Last Edit: 09/09/2018 04:25 PM by brickmack »

Offline jbenton

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Re: Reviving manned Dream Chaser?
« Reply #53 on: 09/09/2018 10:40 PM »
Thanks for that information!

How would it reboost Hubble if it's docked to Dream Chaser's aft? (or anything else, for that matter)

Would it use it's nose mounted RCS thrusters? Is there even enough delta-v for that?

Offline Rocket Science

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Re: Reviving manned Dream Chaser?
« Reply #54 on: 09/10/2018 01:47 PM »
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Online envy887

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Re: Reviving manned Dream Chaser?
« Reply #55 on: 09/11/2018 12:35 PM »
“Flaming meteors of solid propellant” I think was the term used to argue against a capsule on a vehicle using SRBs in case of an abort where the SRBs would have been unzipped, potentially resulting in parachute failure if one struck a chute on the way down.


I hate saying that, because I was a huge Direct fanboy.

I have often wondered about how Starliner and Orion get around that. It helps Starliner, at least, that monolithic solids are inherently safer than segmented ones.


Dream Chaser has an abort motor that is presumably able to maintain attitude control throughout an abort. Also, its compact lifting body design likely allows much higher aerodynamic loading without structural failure compared to the longer, thinner Shuttle.

In an early launch failure especially if the LV has solids DC or any other space plane type vehicle actually has advantage over a capsule in that it doesn't have to worry about having the flaming debris melt it's parachutes.
A TPS covered wing is a lot more resistant to flaming debris than a nylon parachute.
If chutes are still used for an emergency landing scenario it still has a slower drop rate along with more forward travel which gives it more time to wait out the debris cloud and get farther away from it.

 I thought the "flaming meteors of solid propellant" would be a risk for the spacecraft itself too, not just the parachutes. Therefore, I supposed that even DreamChaser would be at risk due to solids, but I suppose I was wrong.
Time under the area of debris impact is important, as is the sensitivity of the vehicle to heat. DreamChaser has more lift and can can glide quickly away from the impact area, while a capsule is going to more or less land in the same place as the debris, but will hand under chutes for several minutes while stuff is falling, unless the abort system is powerful enough to get it further away.

And it's the chutes that are vulnerable to flaming propellant. Both the capsule and spaceplane are covered in TPS that won't have any issues with an open flame. But the chutes can melt and burn.

Impact to the spacecraft is also an issue, but IMO not as significant. Even if the TPS is damaged, the vehicle is unlikely to be travelling fast enough to need a wholly intact TPS to survive reentry (the solids burn out before it reaches those speeds). And propellant chunk impacts probably won't cause significant structural damage to the vehicle.

Offline Patchouli

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Re: Reviving manned Dream Chaser?
« Reply #56 on: 09/13/2018 03:05 AM »

Time under the area of debris impact is important, as is the sensitivity of the vehicle to heat. DreamChaser has more lift and can can glide quickly away from the impact area, while a capsule is going to more or less land in the same place as the debris, but will hand under chutes for several minutes while stuff is falling, unless the abort system is powerful enough to get it further away.

And it's the chutes that are vulnerable to flaming propellant. Both the capsule and spaceplane are covered in TPS that won't have any issues with an open flame. But the chutes can melt and burn.

Impact to the spacecraft is also an issue, but IMO not as significant. Even if the TPS is damaged, the vehicle is unlikely to be travelling fast enough to need a wholly intact TPS to survive reentry (the solids burn out before it reaches those speeds). And propellant chunk impacts probably won't cause significant structural damage to the vehicle.

DC probably has a lift to drag similar to the HL-20 which was around 3.6 to 4.2 depending if flat fins or ones with an airfoil shape are used so it should be able to get well clear the debris cloud even during a T+0 abort.

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