Author Topic: Orbital Access  (Read 7354 times)

Offline john smith 19

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Re: Orbital Access
« Reply #20 on: 09/05/2017 11:07 AM »
STS-51F
I stand corrected. Under certain circumstances the SSME's were indeed able to compensate for small thrust reductions, but one of the reasons mfg the SRBs was tough was to ensure very close thrust balance, which would have only been discovered during SRB ignition. When most people talk about "engine out" they mean throughout most of at least the first stage flight. A sub par thrust level in one of the SRB's would have been impossible to compensate for as they didn't throttle. You can make SRB's throttle, but it's very hard work.

Quote from: JCRM
Yes, the inlet air temperature, after the triple shock acceleration from freestream to Mach 5. Not the skin temperature - Skylon is expected to only reach 1100K on re-entry - with hotter cannards and leading edges.
You have that backward. The air is decelerated in the inlet, which causes the pressure and temperature rises.
I'll note that 1100K is 827C, That's well below the softening temperature of Titanium, but about 60% heavier than Aluminium. Given the design is an air launch assisted TSTO it might be the severe thermal issues that drove REL to go with Pyrosic don't apply

The question would be  how well it would survive short times at very high temperature, very high speed, air flow without burning.

Quote from: JCRM
... at 30,000 meters. it reached about 500C, with some hot spots around twice that The x15 was designed to test re-entry conditions by flying fast and level altitudes- the Orbital 500 isn't designed to test re-entry conditions, so while it briefly does Mach 8 at that altitude before climbing and slowing to Mach 4 at 80km, it is doing that in a blunt body pose, not a streamline one - and on that first hot dip it's below 40km feet for less than 30 seconds.
Except where they got shock/shock interference heating (Edney Type III and Type IV IIRC) where that goes to more like 4:1 or above, which is what sheared off the dummy SCramjet they were testing.
Quote from: JCRM
At the end of the day, this is pointless speculation. If the next stage of the project is funded I'm sure Strathclyde will run their re-entry software over it, refine the shape, then work out what's hot and what's not.
Probably. This is the stage to design out technical risks.

I like the concept, although there are very vague on what engines they are looking at.

I'm more concerned about the business model and the market.

Talk of vast low orbit constellations puts me in mind of Geostar, Orbcomm and Iridium, and not in a good way.  :(
« Last Edit: 09/06/2017 10:46 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline JCRM

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Re: Orbital Access
« Reply #21 on: 09/13/2017 10:23 AM »
STS-51F
I stand corrected. Under certain circumstances the SSME's were indeed able to compensate for small thrust reductions,
The engine was shut down.
Quote from: john smith 19
but one of the reasons mfg the SRBs was tough was to ensure very close thrust balance, which would have only been discovered during SRB ignition.
Careful - you're skirting awfully close to calling a motor an engine.... ;p
Quote from: john smith 19
When most people talk about "engine out" they mean throughout most of at least the first stage flight.
The shuttle was designed to have one engine shut down, and either abort to orbit, or if the loss was too early in the flight to abort once around.

Engine out capability can mean the ability to complete the mission, but I was using it to mean "not fall out of the sky" - which for the Orbital 500 would be gain enough altitude to glide back to a runway.
Quote from: john smith 19
Quote from: JCRM
Yes, the inlet air temperature, after the triple shock acceleration from freestream to Mach 5. Not the skin temperature - Skylon is expected to only reach 1100K on re-entry - with hotter cannards and leading edges.
You have that backward. The air is decelerated in the inlet,
I disagree, but the discrepency is down to a different frame of reference. In flight the air is accelerated (and compressed) from rest to almost the speed of the vehicle. Relative to the engine it's decelerated, in a wind tunnel it's decelerated, and in most ways that matter there isn't a difference
Quote from: john smith 19
Given the design is an air launch assisted TSTO it might be the severe thermal issues that drove REL to go with Pyrosic don't apply
The severe thermal issues are during re-entry, from orbital velocity. The Orbital 500 doesn't have an air intake - unless it's carrying one as part of a test engine replacing the payload bay and engines, at which point the inlet material is the choice of the test engine developers.

The question would be  how well it would survive short times at very high temperature, very high speed air flow without deforming or burning.
Quote from: john smith 19
Quote from: JCRM
... at 30,000 meters. it reached about 500C, with some hot spots around twice that The x15 was designed to test re-entry conditions by flying fast and level altitudes- the Orbital 500 isn't designed to test re-entry conditions, so while it briefly does Mach 8 at that altitude before climbing and slowing to Mach 4 at 80km, it is doing that in a blunt body pose, not a streamline one - and on that first hot dip it's below 40km feet for less than 30 seconds.
Except where they got shock/shock interference heating (Edney Type III and Type IV IIRC) where that goes to more like 4:1 or above, which is what sheared off the dummy SCramjet they were testing.
the lesson here is don't go adding pointy bodies parallel to another that without planning for it. Skylon has the same issue, with it's wingtip nacelles, but they've planned for that and intend to have specialist materials in those areas. Where do you think dual shock interaction may occur on the proposed design?
Quote from: JCRM
At the end of the day, this is pointless speculation. If the next stage of the project is funded I'm sure Strathclyde will run their re-entry software over it, refine the shape, then work out what's hot and what's not.
[/quote]
On reviewing "Vehicle and mission design of a future small payload launcher", the mission design used some crude modelling to control the general heating (pp 8-11), and "A commercially driven design approach to UK future small payload launch systems" claims "an aerothermal model was developed by Fluid Gravity Engineering to calculate the heat loads and
wall    temperatures,    and    to    assess    the    TPS requirements  and  sizing"
Quote from: john smith 19
I like the concept, although there are very vague on what engines they are looking at.
I'd guess that's because they're not yet looking at specific engines - component selection being further along the design process (although with COTS being a priority for the approach, and engine performance being important to the vehicle it seems strange they just estimated an engine)
Now, with that rectangular cross-section wouldn't a linear aerospike look lovely? :p
Quote from: john smith 19
I'm more concerned about the business model and the market.

Talk of vast low orbit constellations puts me in mind of Geostar, Orbcomm and Iridium, and not in a good way.  :(
I find the prediction of nanosat congestion in 15 years rather depressing.
Predicting the future is difficult, but launch rates are rising, and payloads more so, but it's the same business model that all the other small sat launchers are using.

If one were looking to design an airframe to test fly an experimental engine, sharing development costs with a small sat launch system is attractive. Even if the program never turns an overall profit, it only needs to cover the launch costs, and the incremental cost between the test vehicle and the launch vehicle in order for it to have paid for itself and effectively be making money.

Offline ringsider

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Re: Orbital Access
« Reply #22 on: 10/17/2017 10:10 AM »
I'm not sure Orbital Access are still pushing ahead with their planned listing in Malta:

https://www.ft.com/content/a9d0600a-2dfa-11e7-9555-23ef563ecf9a

But given the news today I guess they would not want to be connected to getting funding from there to be honest:

https://www.theguardian.com/world/2017/oct/17/murdered-panama-papers-journalist-son-malta-crooks-daphne-caruana-galizia
« Last Edit: 10/17/2017 10:20 AM by ringsider »

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