Claim: Supergun could have put satellites into Orbit, if the first customer hadn't been Saddam Hussein. [Status: uncertain]

[wumpus]

12 hours ago, DerekL1963 said:

0.o   A gun fired projectile doesn't need to perform a pitch maneuver/gravity turn in the first place, it's not a powered vehicle and doesn't fly like a powered vehicle does.   It needs an attitude control system for the circularization burn.
 

o.0  No, you don't need to be going horizontal or nearly so.  (Though that does minimize the size of your circularization burn.)

Going vertical means you have full (or at least 90% due to decreased gravity in orbit) of your gravity losses the entire flight, including most of your circularization burn.  It also means that your circularization burn is going to be at least the square root of the orbital velocity (assuming you punched through the atmosphere with another square root of to orbital velocity).  You would be better off going somewhat sideways, and using something resembling a pitchover (gliding into an angle).  From memory, the steering losses are equal to the cosine of the angle between prograde and the direction you are firing: in this case they are going to be huge.  You still want a pitchover, and for roughly the same reason.

Another question would be "is there a muzzle velocity that makes sense for firing SRB-based rockets into orbit?  Instead of attempting to fire a projectile all the way to orbit, you would visualize a three stage (SRB-based) rocket, and replace the first stage with a supergun.  Such an system wouldn't be remotely cost effective now (its only possible common mission would likely be ISS resupply, much like any other supergun), but it is likely to make much more sense earlier* than other approaches that eschew rockets at least part of the way (Skylon and others).

* consider building a space elevator.  Presumably the [carbon nanotube] "rope" could withstand arbitrary g forces, and you needed to launch a lot into space before you had a working space elevator.  It might even work for chucking fuel into space (for large values of "if", such as a reasonably low cost gun, and really cheap SRBs (much lower size means easy transportation, dirt cheap cargo implies simplified construction [if it explodes, so what]).  I'm guessing from the excess number of small satellite launchers and the lack of SRB-based solutions they use, building small SRBs don't give you enough of a scaling advantage (something I've seen here as a reason why you don't see many SRBs), and don't expect a quick and dirty SRB to be sufficiently cheap.

[DerekL1963]

1 hour ago, wumpus said:

I'm guessing from the excess number of small satellite launchers and the lack of SRB-based solutions they use, building small SRBs don't give you enough of a scaling advantage (something I've seen here as a reason why you don't see many SRBs), and don't expect a quick and dirty SRB to be sufficiently cheap.

It's partly that, partly that handling significant amounts of explosives solid rockets is rather more difficult.  Finding a site to manufacture explosives build the mixing and pouring facilities is a challenge as opposed to unfuelled liquid stages, which are inert.   Transporting explosives them from factory to the launch site requires a metric [censored] ton of permits and paper, while unfuelled liquids can simply be tossed on the back of a truck.  Once at the launch site, solids are much, much heavier and increasing handling difficulty.  Etc... etc...

[wumpus]

1 hour ago, DerekL1963 said:

It's partly that, partly that handling significant amounts of explosives solid rockets is rather more difficult.  Finding a site to manufacture explosives build the mixing and pouring facilities is a challenge as opposed to unfuelled liquid stages, which are inert.   Transporting explosives them from factory to the launch site requires a metric [censored] ton of permits and paper, while unfuelled liquids can simply be tossed on the back of a truck.  Once at the launch site, solids are much, much heavier and increasing handling difficulty.  Etc... etc...

While all this is true, it is pretty pedantic to suggest that liquid oxygen is anything but an explosive.  It might not be, but it can make virtually anything it touches an explosive (charcoal + LOX is a favorite industrial explosive.  If the detonator fails, just wait for the thing to be a dud detonator (still dangerous) and a pile of charcoal (not so much)).

For all the Hindenburg's ability to be remembered, explosiveness isn't a big problem of hydrogen (everything else is).

I'm also guessing that building a SRB construction site near either Cape Canaveral (probably inhabited, extreme issues in digging a bunker) or Vandenburg (if there is an area nearby that isn't heavily inhabited, it will be) just aren't good places to build an SRB.  They might do better if Spaceport America had a chance to take off (what were they thinking?).

* I think Wallops has issues mostly like Canaveral.  You would have to pretty far inland to dig a bunker, and anywhere on the coast is prime real estate.  Considering I live in Maryland, it is embarrassing to forget that one.

[PB666]

On 3/21/2016 at 8:57 PM, Nothalogh said:

Yep, spaceguns sound appealing, until you figure out how orbit works

Correct, about the first thing in the thread, it gets the projectile into space at 2-3 km/sec for muzzle velocity. The problem is that at apogee it needs something to circularize the orbit, that means an additional 6 km/s of dv.

Consider 3000 m/s at 9.8 meter sec = 300, if you launch at a 45' angle that 0.707 then radial vector is 2121 m/s that only give 215 seconds of time.

The horizontal velocity is only 2121 and the needed circularization velocity is 6483000 m therefore speed required is mu =398,575,072,480,000    V = SQRT(mu/6483000) = 7800

This means it climbs to an altitude of slightly more than = 4.9 * T*2 = 226,500 meters (this is without factoring out significant drag), at that altitude an additional

7800-2100 dv to achieve orbit, that is a majority of the velocity it would take (5700 m/s). At 2 g it would take 285 seconds. Consequently after launch it would take  142.5 seconds prior to apogee to  burn orbitally apogee to successfully obtain orbit, That means 70 seconds after launch at an altitude of approximately 130km (not a bad altitude for burning on a space thruster) you would need to burn about 280 seconds  at 2 g parallel to the surface of the earth. Thats actually kind of a long burn but for a modern second stage engine with good ISP its not to bad. Problem is you are talking about tons of mass, and more than a meter in diameter, the walls of the gun would have to be thick. 

 

[DerekL1963]

3 hours ago, wumpus said:

4 hours ago, DerekL1963 said:

It's partly that, partly that handling significant amounts of explosives solid rockets is rather more difficult.  Finding a site to manufacture explosives build the mixing and pouring facilities is a challenge as opposed to unfuelled liquid stages, which are inert.   Transporting explosives them from factory to the launch site requires a metric [censored] ton of permits and paper, while unfuelled liquids can simply be tossed on the back of a truck.  Once at the launch site, solids are much, much heavier and increasing handling difficulty.  Etc... etc...

While all this is true, it is pretty pedantic to suggest that liquid oxygen is anything but an explosive.  It might not be, but it can make virtually anything it touches an explosive (charcoal + LOX is a favorite industrial explosive.  If the detonator fails, just wait for the thing to be a dud detonator (still dangerous) and a pile of charcoal (not so much)).

Be that as that may be...  But you miss a critical difference from the point of view of the smallsat launcher operator.   Said operator has to pretty much provide everything when it comes to solid fuels.   Liquid fuels and LOX are black boxes though - a phone call and credit card info go in one side, and LOX and fuel come out the other.  If there's an accident with either in production or transport, it's the fuel (or LOX) provider or the transport company that have to deal with it.

[fredinno]

8 hours ago, wumpus said:

Going vertical means you have full (or at least 90% due to decreased gravity in orbit) of your gravity losses the entire flight, including most of your circularization burn.  It also means that your circularization burn is going to be at least the square root of the orbital velocity (assuming you punched through the atmosphere with another square root of to orbital velocity).  You would be better off going somewhat sideways, and using something resembling a pitchover (gliding into an angle).  From memory, the steering losses are equal to the cosine of the angle between prograde and the direction you are firing: in this case they are going to be huge.  You still want a pitchover, and for roughly the same reason.

Another question would be "is there a muzzle velocity that makes sense for firing SRB-based rockets into orbit?  Instead of attempting to fire a projectile all the way to orbit, you would visualize a three stage (SRB-based) rocket, and replace the first stage with a supergun.  Such an system wouldn't be remotely cost effective now (its only possible common mission would likely be ISS resupply, much like any other supergun), but it is likely to make much more sense earlier* than other approaches that eschew rockets at least part of the way (Skylon and others).

* consider building a space elevator.  Presumably the [carbon nanotube] "rope" could withstand arbitrary g forces, and you needed to launch a lot into space before you had a working space elevator.  It might even work for chucking fuel into space (for large values of "if", such as a reasonably low cost gun, and really cheap SRBs (much lower size means easy transportation, dirt cheap cargo implies simplified construction [if it explodes, so what]).  I'm guessing from the excess number of small satellite launchers and the lack of SRB-based solutions they use, building small SRBs don't give you enough of a scaling advantage (something I've seen here as a reason why you don't see many SRBs), and don't expect a quick and dirty SRB to be sufficiently cheap.

Oh really? So Pegasus and SPARK are not smallsat launchers? (not to mention VEGA, Minotaur-C, and Athena, if your definition of "smallsat launcher" is a little higher) All right then. Seriously, the only nanosat launchers (less than 1T) operational in the west (not sure about the east, but https://en.wikipedia.org/wiki/Long_March_11 is also a solid-fueled smallsat launcher currently running) are solids. Not to mention the small SRB line of the Delta SRBs and STAR.

My guess is that the liquid-fueled smallsat launcher developers want better performance or the ability to reuse it via chutes later.

4 hours ago, wumpus said:

While all this is true, it is pretty pedantic to suggest that liquid oxygen is anything but an explosive.  It might not be, but it can make virtually anything it touches an explosive (charcoal + LOX is a favorite industrial explosive.  If the detonator fails, just wait for the thing to be a dud detonator (still dangerous) and a pile of charcoal (not so much)).

For all the Hindenburg's ability to be remembered, explosiveness isn't a big problem of hydrogen (everything else is).

I'm also guessing that building a SRB construction site near either Cape Canaveral (probably inhabited, extreme issues in digging a bunker) or Vandenburg (if there is an area nearby that isn't heavily inhabited, it will be) just aren't good places to build an SRB.  They might do better if Spaceport America had a chance to take off (what were they thinking?).

* I think Wallops has issues mostly like Canaveral.  You would have to pretty far inland to dig a bunker, and anywhere on the coast is prime real estate.  Considering I live in Maryland, it is embarrassing to forget that one.

Well, neither launch site is a great place to build liquid rocket tanks either...

1 hour ago, DerekL1963 said:

Be that as that may be...  But you miss a critical difference from the point of view of the smallsat launcher operator.   Said operator has to pretty much provide everything when it comes to solid fuels.   Liquid fuels and LOX are black boxes though - a phone call and credit card info go in one side, and LOX and fuel come out the other.  If there's an accident with either in production or transport, it's the fuel (or LOX) provider or the transport company that have to deal with it.

Not really, there are SRB manufactures like ATK and Aerojet. You don't have to provide everything when it comes to solid fuels- liquids are actually worse n that sense because you need to build the tanks in either a rented or newly built facility and need more complex infrastructure.

[PB666]

20 hours ago, wumpus said:

* consider building a space elevator.  Presumably the [carbon nanotube] "rope" could withstand arbitrary g forces, and you needed to launch a lot into space before you had a working space elevator.  It might even work for chucking fuel into space (for large values of "if", such as a reasonably low cost gun, and really cheap SRBs (much lower size means easy transportation, dirt cheap cargo implies simplified construction [if it explodes, so what]).  I'm guessing from the excess number of small satellite launchers and the lack of SRB-based solutions they use, building small SRBs don't give you enough of a scaling advantage (something I've seen here as a reason why you don't see many SRBs), and don't expect a quick and dirty SRB to be sufficiently cheap.

Nope. Nothing strong enough to hang from 45,000,000 meters

[fredinno]

8 hours ago, PB666 said:

Nope. Nothing strong enough to hang from 45,000,000 meters

...yet.