For Questions That Don't Merit Their Own Thread

[RyanRising]

I’ve seen a few mentions of how the SSMEs couldn’t be relit in flight, but I don’t immediately see why that is. My understanding is they use a spark to ignite a blowtorch to ignite the rest of the fires that power the engine, without any special ignition resources (anything besides electricity, hydrogen, and oxygen.) So if you still have fuel, oxidiser, and electricity onboard, and you have an engine that’s designed to work again after the flight, why couldn’t it start up again during it? 

[p1t1o]

1 hour ago, RyanRising said:

I’ve seen a few mentions of how the SSMEs couldn’t be relit in flight, but I don’t immediately see why that is. My understanding is they use a spark to ignite a blowtorch to ignite the rest of the fires that power the engine, without any special ignition resources (anything besides electricity, hydrogen, and oxygen.) So if you still have fuel, oxidiser, and electricity onboard, and you have an engine that’s designed to work again after the flight, why couldn’t it start up again during it? 

Im not sure exactly, but I imagine it is to do with various gas-dynamic and thermal issues with flushing cryogenic gases through hot metal parts, in variable external pressure conditions, with turbopumps that have just been in some quite horrific conditions. I think engines have to be specifically designed to be re-startable (and even then its not as easy as on/off/on/off). Parts are designed to be used under certain conditions, like temperatures, pressures and mechanical stresses - and a steady-state is much easier to withstand than a variable state. The answer may be as simple as it was not designed to be reusable because it was not required and to save weight.

1 hour ago, RyanRising said:

you have an engine that’s designed to work again after the flight

Only after some very extensive refurbishing, and only for a few flights per engine.

[DDE]

5 hours ago, RyanRising said:

I’ve seen a few mentions of how the SSMEs couldn’t be relit in flight, but I don’t immediately see why that is. My understanding is they use a spark to ignite a blowtorch to ignite the rest of the fires that power the engine, without any special ignition resources (anything besides electricity, hydrogen, and oxygen.) So if you still have fuel, oxidiser, and electricity onboard, and you have an engine that’s designed to work again after the flight, why couldn’t it start up again during it? 

Quote

There are three common ways for starting a [liquid-propellant rocket engine] with a [turbopump]; a "tank head" start and two types of "spin-up" start. This tank head is the elevation of the liquid level above the pump inlet plus the head equivalent of the gas pressure in the propellant tank. It is a pressure, and it is expressed in meters or feet as the height of an equivalent column of liquid. With the low tank head as the ini-tial pressure, the gas generator or preburner will have a low initial flow of warm gas, and it will take several seconds for the warm gas to spin the turbine and boot strap it up to full speed. This type of tank head start is used on the Rocketdyne F-l engine shown in Fig. 7.8-10 and the MA-3 Atlas engine shown in Fig. 7.8-5 and the SSME shown in Figs. 7.8-17 and 7.8-18. The starting procedure for the SSME using a tank head start is described on page 401 of the seventh edition of Ref. 4. Although a tank head start can last 3 to 5 s for a large LPRE, the amount of propellant used is relatively small because most of this start period is at very low flow.

...

Some form of external power can be applied temporarily during the start to accelerate the spin up of the TP to full power. This is the other way of starting a pump-fed LPRE. For large LPREs this will shorten the time for the start transient by a factor of two or three. The earliest form of this external power was compressed air from an external source (such as a ground-based compressor or high-pressure storage tank), and this air was put into the turbine inlet manifold. Goddard used compressed air to start the tests for his first TPs (1938), and other LPREs have used these in-ground tests as a starting method in the 1940s and sporadically thereafter. The Rocketdyne J-2 LOX/LH2 engine, described in Chapter 7.8, carries a tank of high-pressure hydrogen gas for starting and restarting the rotation of its two turbines. This spherical tank can be seen as a part of the engine in Fig. 7.8-13 and 7.8-14.

SpaceX use helium.

[magnemoe]

14 hours ago, p1t1o said:

Im not sure exactly, but I imagine it is to do with various gas-dynamic and thermal issues with flushing cryogenic gases through hot metal parts, in variable external pressure conditions, with turbopumps that have just been in some quite horrific conditions. I think engines have to be specifically designed to be re-startable (and even then its not as easy as on/off/on/off). Parts are designed to be used under certain conditions, like temperatures, pressures and mechanical stresses - and a steady-state is much easier to withstand than a variable state. The answer may be as simple as it was not designed to be reusable because it was not required and to save weight.

Only after some very extensive refurbishing, and only for a few flights per engine.

Pretty much, space shuttle and most engines with gas fuel and oxidizer uses an small chamber with an spark plug, you inject fuel and oxygen gas into this and the blowtorch out of this ignite the rocket engine. 
And yes the space shuttle engine was not designed to be restarted simply as it was no need. You could probably have designed it so it could be restarted but it would complicated them and it was no need
Only three of the falcon 9 first stage engines can be restarted as in is not set up for for the restarting fluid. 

[magnemoe]

11 hours ago, DDE said:

  15 hours ago, RyanRising said:

I’ve seen a few mentions of how the SSMEs couldn’t be relit in flight, but I don’t immediately see why that is. My understanding is they use a spark to ignite a blowtorch to ignite the rest of the fires that power the engine, without any special ignition resources (anything besides electricity, hydrogen, and oxygen.) So if you still have fuel, oxidiser, and electricity onboard, and you have an engine that’s designed to work again after the flight, why couldn’t it start up again during it? 

  Quote

There are three common ways for starting a [liquid-propellant rocket engine] with a [turbopump]; a "tank head" start and two types of "spin-up" start. This tank head is the elevation of the liquid level above the pump inlet plus the head equivalent of the gas pressure in the propellant tank. It is a pressure, and it is expressed in meters or feet as the height of an equivalent column of liquid. With the low tank head as the ini-tial pressure, the gas generator or preburner will have a low initial flow of warm gas, and it will take several seconds for the warm gas to spin the turbine and boot strap it up to full speed. This type of tank head start is used on the Rocketdyne F-l engine shown in Fig. 7.8-10 and the MA-3 Atlas engine shown in Fig. 7.8-5 and the SSME shown in Figs. 7.8-17 and 7.8-18. The starting procedure for the SSME using a tank head start is described on page 401 of the seventh edition of Ref. 4. Although a tank head start can last 3 to 5 s for a large LPRE, the amount of propellant used is relatively small because most of this start period is at very low flow.

...

Some form of external power can be applied temporarily during the start to accelerate the spin up of the TP to full power. This is the other way of starting a pump-fed LPRE. For large LPREs this will shorten the time for the start transient by a factor of two or three. The earliest form of this external power was compressed air from an external source (such as a ground-based compressor or high-pressure storage tank), and this air was put into the turbine inlet manifold. Goddard used compressed air to start the tests for his first TPs (1938), and other LPREs have used these in-ground tests as a starting method in the 1940s and sporadically thereafter. The Rocketdyne J-2 LOX/LH2 engine, described in Chapter 7.8, carries a tank of high-pressure hydrogen gas for starting and restarting the rotation of its two turbines. This spherical tank can be seen as a part of the engine in Fig. 7.8-13 and 7.8-14.

SpaceX use helium.

Do you have an link to the article? it looks interesting. 

And the tank head pressure solution would not work well in space as you don't have much of an head pressure also it looks like its some startup time. Using gas sounds better here and it was also done for Saturn 5 3rd stage who needed restart. 
Anybody know how raptor solves this. My guess is that they use the high pressure methane and oxygen gas. 

And again SpaceX was very lucky, they needed merlin to be restartable because upper stage. 

[DDE]

4 hours ago, magnemoe said:

Do you have an link to the article? it looks interesting. 

It's Sutton's 700-page seminal History of Liquid-Propellant Rocket Engines. A moderator of r/space dropped a link to a .pdf scan many, many moons ago. Not even sure if it's actually legal to distribute it like that...

4 hours ago, magnemoe said:

Anybody know how raptor solves this. My guess is that they use the high pressure methane and oxygen gas. 

I know they have additional header tanks, maybe even like the Agena, with some sort of physical separation between the liquid propellant and the pressurant gas...

[ARS]

Does an ICBM is sturdier than normal launch vehicles? I assume since they are military grade hardware for launching nukes on suborbital trajectory over enemy territory, I expect them to be armored or at least more durable than regular rockets

[magnemoe]

1 hour ago, ARS said:

Does an ICBM is sturdier than normal launch vehicles? I assume since they are military grade hardware for launching nukes on suborbital trajectory over enemy territory, I expect them to be armored or at least more durable than regular rockets

Yes they are sturdier, mostly because they have to be stored for decades, they must also be able to launch in all weather. Most are solid fuel who are sturdier. Not armored in any way other than standard SRB tubing and an pretty sturdy fairing because of all weather launch. 
The submarine ones are even launched from below water. 
Warhead also has to survive reentry, however if you are hit by an anti ballistic missile in space armor does not help much, even if you was build in an way who made you survive the impact, say an armor piecering battleship shell was able too it would not help you much as you are knocked off course, your front is no longer symmetrical and aerodynamic and the shock would shatter the bomb anyway. 

[K^2]

Yeah, outside of what's needed to survive the launch, they don't have any physical protection. Some warheads are designed to maneuver in atmosphere on re-entry, though.

[JoeSchmuckatelli]

On 7/3/2020 at 7:45 AM, Spacescifi said:

 

Reality is often superior to scifi tropes. 

I just wanted to know if human soldiers could actually stand a chance against dedicated remote small war machines.

The answer is probably no.

Inasmuch throughout history man has designed more efficient ways of conducting wars.

Other than placing tons of IED's ahead of the land drones I don't know how scifi soldiers would deal with them wiithout taking heavy casualties.

They have no answer beyond shotguns against flying armed drones.

 

I don't know if you have any combat experience... But my perception of humans vs drones is that the humans win.  Not in every fight, but over time people win. 

I've spent time as an infantry officer and a tank officer.  I can tell you that the ingenuity, tenacity and pure destructive will of 20-somethings is impressive. I would never bet against humans in that fight.  Even if the drones are operated by AF weenies. 

What you are describing is the armor vs infantry debate.  It's an argument that's been raging since the introduction of... well shiz, the horse... Or wait - actually before: We've introduced literally generations of war-ending, human defeating 'Ultimate Weapons' since Thak first strapped a rock to a stick. 

 

[DDE]

16 hours ago, ARS said:

Does an ICBM is sturdier than normal launch vehicles? I assume since they are military grade hardware for launching nukes on suborbital trajectory over enemy territory, I expect them to be armored or at least more durable than regular rockets

ICBMs are to a certain degree hardened against nuclear detonations in proximity to the silo, and against nearby explosions during atmosoheric ascent. Certain SLBMs, specifically the Bark, were designed for launch below ice, and so even with an ice-breaching charge they'd have to overcome a lot of debris during the submerged part of 'flight'.

[JoeSchmuckatelli]

1 hour ago, DDE said:

ICBMs are to a certain degree hardened against nuclear detonations in proximity to the silo, and against nearby explosions during atmosoheric ascent. Certain SLBMs, specifically the Bark, were designed for launch below ice, and so even with an ice-breaching charge they'd have to overcome a lot of debris during the submerged part of 'flight'.

This.

 

We also have ground penetrating delayed detonation warheads... Tailor made for those pesky hardened C&C bunkers. 

But I think that for pure reentry purposes the smaller size and lack of need to protect a human crew makes them 'sturdier' without any specific need to worry about military grade 'hardening' beyond what DDE described - and mostly that is not to protect the warhead from reentry, but rather to go boom when we want it to... Not bc something else went boom nearby 

[Spacescifi]

5 hours ago, JoeSchmuckatelli said:

I don't know if you have any combat experience... But my perception of humans vs drones is that the humans win.  Not in every fight, but over time people win. 

I've spent time as an infantry officer and a tank officer.  I can tell you that the ingenuity, tenacity and pure destructive will of 20-somethings is impressive. I would never bet against humans in that fight.  Even if the drones are operated by AF weenies. 

What you are describing is the armor vs infantry debate.  It's an argument that's been raging since the introduction of... well shiz, the horse... Or wait - actually before: We've introduced literally generations of war-ending, human defeating 'Ultimate Weapons' since Thak first strapped a rock to a stick. 

 

 

Prep time is the only way infantry has a chance.

Since they will be on the defensive the whole time regardless.

 

Infantry is basically a mobile self targeting turret with limited ammo... that's it.

With prep they get put up defensive screens to slow the onslaught while sniping back.

 

Infantry could actually wreck land drobes with prep I will admit.

It's the flying support drones that will actually start hyrting infantry morale.

 

Being out in the open invites targeting via flying drones.

Sheltering somewhere invites multiple drones pummel said shelter with missiles.

There is no escape for infantry, their only chance is fighting back with weaponry that can kill rhe drones with efficiebt firepower.

[JoeSchmuckatelli]

10 minutes ago, Spacescifi said:

 

Prep time is the only way infantry has a chance.

Since they will be on the defensive the whole time regardless.

 

Infantry is basically a mobile self targeting turret with limited ammo... that's it.

With prep they get put up defensive screens to slow the onslaught while sniping back.

 

Infantry could actually wreck land drobes with prep I will admit.

It's the flying support drones that will actually start hyrting infantry morale.

 

Being out in the open invites targeting via flying drones.

Sheltering somewhere invites multiple drones pummel said shelter with missiles.

There is no escape for infantry, their only chance is fighting back with weaponry that can kill rhe drones with efficiebt firepower.

And yet our most recent experience with combat using drones, gunships and every other high tech etc against infantry proves otherwise. C. F. AFGHANISTAN. 

 

We used to have a saying in the Marines. 'The Air Force can drop bombs on a target all day, but you don't own it until a 19 year old Lance Corporal is standing on it holding an M-16.

 

If your theory were correct - we would have finished with Afghanistan back in 2003 at the latest. 

 

FYI getting people to agree that they are beaten is a lot tougher than some folks realize 

Edited July 11, 2020 by JoeSchmuckatelli

[Spacescifi]

33 minutes ago, JoeSchmuckatelli said:

And yet our most recent experience with combat using drones, gunships and every other high tech etc against infantry proves otherwise. C. F. AFGHANISTAN. 

 

We used to have a saying in the Marines. 'The Air Force can drop bombs on a target all day, but you don't own it until a 19 year old Lance Corporal is standing on it holding an M-16.

 

If your theory were correct - we would have finished with Afghanistan back in 2003 at the latest. 

 

But getting people to agree that they are beaten is a lot tougher than some folks realize 

 

I know... I am talking about drones that are better than modern ones.

Longer operational periods and better armed too while being smaller a target too.

Convincing a city to just give up?

Remember siege warfare?

In addition to that, with drones one can do a lot of unethical stuff a soldier may think twice about doing.

Namely... there are ways to get people to surrender that WILL break international law, but it only depends on how far the drone operators are willing to go.

And in scifi?

Whatever it takes... which is scary for infantry.

What is infantry vulnerable too?

Chemical. Biological. Psychological. And physical attack. And the need to eat and sleep.l, plus more like emotional and likely more still I never mentioned.

Drones only have three big vulnerabilities I am aware of.

Power. Communication. And physical attack.

 

 

Edited July 11, 2020 by Spacescifi

[JoeSchmuckatelli]

35 minutes ago, Spacescifi said:

 

I know... I am talking about drones that are better than modern ones.

Longer operational periods and better armed too while being smaller a target too.

Convincing a city to just give up?

Remember siege warfare?

In addition to that, with drones one can do a lot of unethical stuff a soldier may think twice about doing.

Namely... there are ways to get people to surrender that WILL break international law, but it only depends on how far the drone operators are willing to go.

And in scifi?

Whatever it takes... which is scary for infantry.

What is infantry vulnerable too?

Chemical. Biological. Psychological. And physical attack. And the need to eat and sleep.l, plus more like emotional and likely more still I never mentioned.

Drones only have three big vulnerabilities I am aware of.

Power. Communication. And physical attack.

 

 

With full awareness that I'm quibbling with your fiction writing - where you can create any reality for your characters that you need to tell your story... 

 

My first observation is that you are merely replacing modern human soldiers - whether infantry, tankers or fliers with a drone analog.  Regardless of the technology - it sounds like analogs of the current world... And again I will point out that absent the sci fi aspect, in the current Era the most powerful and experienced /professionals in the history of humanity have largely failed to change the reality on the ground against a completely mismatched force of infantry. 

 

This, as you pointed out, because we refuse to do what it takes to just kill everyone. And in your story - if your drone army is willing to do anything without regard to the laws of war or political consequences (etc) - then why not just nuke the whole area?  Chernyobil and the Bikini Atols show that nukes are not going to prevent life from returning. 

 

Back to Afghanistan - the only way America could have won was to do to the people of Afghanistan what we did with the Native Americans - supplant them.  With Iraq, perhaps, an analog to the post-war German and Japanese occupation might have succeeded - but short of absolute Colonial control and mass immigration, Afghanistan was never a winnable war

[ARS]

What are these aircrafts?

The big 6-engined bomber

This one has contra-rotating propeller

This one has an intake underneath the propeller (like P-40 Warhawk) and gunner on the rear of the cockpit

And this one

[DDE]

4 hours ago, ARS said:

The big 6-engined bomber

Six engines in a tractor configuration almost certainly means an Axis Amerikabomber project. All the German designs had a B-24-esque twin tail and a charecteristingly outdated defense gun arrangement (e.g. in a rear-firing chin blister).

I'm calling it one of the Nakajima G10N-related studies, which seem to have had predominantly American-style turrets as implied by the Renzan, Japan's B-17 emulation, and, at least in Navy's proposals, a single tail:

The stepped cockpit is, however, stolen off of a Ju 390:

5 hours ago, ARS said:

And this one

Blisters match a Mitsubishi Ki-67.

[JoeSchmuckatelli]

7 hours ago, ARS said:

What are these aircrafts?

The big 6-engined bomber

This one has contra-rotating propeller

This one has an intake underneath the propeller (like P-40 Warhawk) and gunner on the rear of the cockpit

And this one

I don't know the aircraft - but it looks like either WarThunder or World of WarPlanes - and their game sites have a ton of information about real and speculation aircraft 

[Spacescifi]

16 hours ago, JoeSchmuckatelli said:

With full awareness that I'm quibbling with your fiction writing - where you can create any reality for your characters that you need to tell your story... 

 

My first observation is that you are merely replacing modern human soldiers - whether infantry, tankers or fliers with a drone analog.  Regardless of the technology - it sounds like analogs of the current world... And again I will point out that absent the sci fi aspect, in the current Era the most powerful and experienced /professionals in the history of humanity have largely failed to change the reality on the ground against a completely mismatched force of infantry. 

 

This, as you pointed out, because we refuse to do what it takes to just kill everyone. And in your story - if your drone army is willing to do anything without regard to the laws of war or political consequences (etc) - then why not just nuke the whole area?  Chernyobil and the Bikini Atols show that nukes are not going to prevent life from returning. 

 

Back to Afghanistan - the only way America could have won was to do to the people of Afghanistan what we did with the Native Americans - supplant them.  With Iraq, perhaps, an analog to the post-war German and Japanese occupation might have succeeded - but short of absolute Colonial control and mass immigration, Afghanistan was never a winnable war

 

Reasons why not to just nuke a city?

1. Want to keep it intact for remaining population.

2.  I see drones as a peacekeeping force kind of like the black hawk down fiasco, only with drones replacing most of the soldiers.

 

Another thought comes to mind regarding conquest in scifi, which HAS been done literally in ancient times.

Some conquerors denied the conquered the right to bear arms (swords).

In scifi they could simply use soldiers and drones to flush out and confiscate all guns they can find,,and then have drones patrol 24/7.

I know this is dystopian... but it is possible tactically.

Assuming flying drones were used for all types of business and delivery and common place, the populace would not be so annoyed by the police and military ones overtime.

[Shpaget]

On 7/9/2020 at 12:21 AM, Spacescifi said:

 

Wow... thank you.

 

So at what range would a steel space vessel be icinerated? Three or 20 kilometers?

At what range could a steel vessel survive with a charred hull? 500 kilometers? 550? 600?

Thanks.

Funnily enough, Scott Manley might have an answer for you.

https://www.youtube.com/watch?v=by1xpy8ob8E

Keep in mind that these balls were placed very close to the bomb, and destructive power drops faster than linearly with distance.

Edited July 13, 2020 by Shpaget

[ARS]

So... This is Bisnovat SK-1, an aircraft, built by USSR in 1938. It's intended to be used as a test bed for research into high speed flight

I am really curious how the pilot has forward visibility with that cockpit design since it looks like there's no forward facing point of view of the cockpit canopy. Anyone knows anything about it? Thanks

[DDE]

2 hours ago, ARS said:

So... This is Bisnovat SK-1, an aircraft, built by USSR in 1938. It's intended to be used as a test bed for research into high speed flight

I am really curious how the pilot has forward visibility with that cockpit design since it looks like there's no forward facing point of view of the cockpit canopy. Anyone knows anything about it? Thanks

The pilot was supposed to be lifted upwards along with some portion if the canopy for landing. The aircraft proved flyable... But, judging from SK-2, no-one else thought it was a good idea:

However, there are ways. Aside from Sukhoi T-4 where the drooping nose would reveal the windshield for landings,

two-seat MiGs have periscopes.

[K^2]

First time I got into a cockpit of a WWII era plane and was asked to taxi, my response was, "How???" Even with conventional, raised cockpit, the nose-up attitude on the ground means you can't see in front of you. Solution? You weave a bit of a snaking pattern when you need to see forward, looking either left of or right of engine in turn. Naturally, it's not the sort of thing I would want to do while landing, but it works on the taxiway.

[ARS]

Does aircraft bombs actually "whistle" when dropped from aircraft? Quite frequently, in movies and video games (especially if set on WW2 era, but sometimes extend to modern era), the bombs are depicted as whistling as it's released from aircraft until impact (most commonly during carpet bomb scene). What's the cause of that whistle?