-
#260
by
acsawdey
on 01 Jul, 2015 19:18
-
I take it the energy added by pumping is so small it wouldn't add even one second of isp?
Higher chamber pressure helps because you can use a larger area ratio without becoming excessively over-expanded at sea level, which then helps the vacuum Isp. However if we're assuming the area ratio is fixed at 12:1 based on estimates from photographs, then increasing chamber pressure doesn't help much. You put energy in when you pump up to the chamber pressure, and you get much of that back from the expansion, however the pump isn't 100% efficient and I don't know what other second order factors come into play.
-
#261
by
jamesh9000
on 01 Jul, 2015 22:43
-
I live in Christchurch! If this actually happens I can go out and take photos and videos. But, like all space startups, I'm not holding my breath. Really hoping this goes ahead though.
-
#262
by
TrevorMonty
on 02 Jul, 2015 02:59
-
Here is a more informative article from spacenews.
http://spacenews.com/rocket-lab-selects-new-zealand-launch-site/Still targetting end of year launch.
The launch facilities shouldn't take to long to build looking at artists drawing. Obtaining resource consent maybe an issue, only takes one determined person opposing it to throw a spanner in the works.
-
#263
by
MATTBLAK
on 02 Jul, 2015 03:26
-
-
#264
by
gin455res
on 02 Jul, 2015 16:55
-
I take it the energy added by pumping is so small it wouldn't add even one second of isp?
Higher chamber pressure helps because you can use a larger area ratio without becoming excessively over-expanded at sea level, which then helps the vacuum Isp. However if we're assuming the area ratio is fixed at 12:1 based on estimates from photographs, then increasing chamber pressure doesn't help much. You put energy in when you pump up to the chamber pressure, and you get much of that back from the expansion, however the pump isn't 100% efficient and I don't know what other second order factors come into play.
I meant the electro-chemical energy added to the propellants that was in the batteries, which is going to theoretically increase the ISP. Normally, pumps take the energy from the propellant. The electric pump doesn't. But the energy density of the batteries is still tiny compared to the energy density of kerosene, even when you divide it be 3-4 (to account for the oxidiser weight). I was just wondering if it would be measurable?
-
#265
by
gin455res
on 02 Jul, 2015 17:21
-
I wonder if having a large battery pack in orbit would enable any 'pulsed' (once per n orbits) hybrid electro-thermal/chemical systems.
for example:
1)The battery pack is charged by some robust solar panels, once full, slightly before perigee some nitrogen N2O4 is pumped through an electro-thermal heater and decomposed into hot pressurised NO2, this is then burnt with fuel.
2) same idea but with ammonia being pressurised and disassociated electro-thermally before combustion with an oxidizer.
-
#266
by
acsawdey
on 02 Jul, 2015 18:44
-
I meant the electro-chemical energy added to the propellants that was in the batteries, which is going to theoretically increase the ISP. Normally, pumps take the energy from the propellant. The electric pump doesn't. But the energy density of the batteries is still tiny compared to the energy density of kerosene, even when you divide it be 3-4 (to account for the oxidiser weight). I was just wondering if it would be measurable?
Sure. Consider a gas-generator cycle: the propellants burned in the gas generator then have some energy extracted by the power turbine that drives the pumps, and further may not be expanded nearly as much as propellant burned in the main combustion chamber. So the exhaust velocity from the gas generator stream will be lower than the main combustion stream. The Isp will be reduced by this, compared to the electric pump where the energy to run the pumps is coming from an external source and all the propellant is burned in the main combustion chamber.
The most extreme example to give might be a nuclear thermal rocket. Here you have a component (nuclear core) that contributes to the weight of the engine but does not lose weight (ok, a tiny amount of mass is converted to energy by the fission or fusion reactions). So, this mass, like that of the batteries, contributes to the engine mass and reduces thrust/weight ratio but does not figure in Isp.
Now, what would be nifty for the battery system would be to use some kind of flow battery system where the spent electrolytes could be dumped or even burned or vaporized in the engine somehow for additional mass flow and more thrust.
-
#267
by
TrevorMonty
on 03 Jul, 2015 01:03
-
-
#268
by
Katana
on 03 Jul, 2015 04:04
-
I wonder if having a large battery pack in orbit would enable any 'pulsed' (once per n orbits) hybrid electro-thermal/chemical systems.
for example:
1)The battery pack is charged by some robust solar panels, once full, slightly before perigee some nitrogen N2O4 is pumped through an electro-thermal heater and decomposed into hot pressurised NO2, this is then burnt with fuel.
2) same idea but with ammonia being pressurised and disassociated electro-thermally before combustion with an oxidizer.
Electro thermal hydrazine thrusters has been used on satellite for decades.
-
#269
by
gin455res
on 05 Jul, 2015 10:02
-
I wonder if having a large battery pack in orbit would enable any 'pulsed' (once per n orbits) hybrid electro-thermal/chemical systems.
for example:
1)The battery pack is charged by some robust solar panels, once full, slightly before perigee some nitrogen N2O4 is pumped through an electro-thermal heater and decomposed into hot pressurised NO2, this is then burnt with fuel.
2) same idea but with ammonia being pressurised and disassociated electro-thermally before combustion with an oxidizer.
Electro thermal hydrazine thrusters has been used on satellite for decades.
sure: eg
http://soliton.ae.gatech.edu/people/jseitzma/classes/ae6450/electrothermal_thrusters.pdfHowever, I'm not sure they (resistojets) have isp-s any better than pure chemical propulsion.
I was more interested in exploring whether there was a regime slightly better than chemical with isp perhaps 400-550 that would normally be low thrust and undone by the Oberth-effect (because of continuous operation), which could benefit from a pulsed perigee burn. And as the extra energy is coming from batteries, which have rubbish storage capacities, and because energy scales with the square of velocity, it seemed to me that as long as such a pulsed system achieved only marginally better performance than chemical, it might be worth-while. Keeping it marginally better reduces energy requirements and length of time for orbit raising.
Using endothermic reactions would allow the extra energy to be added at lower temperatures and so reduce materials requirements.
Having a decent sized battery pack gratis in orbit might allow slightly larger thrusters than the very small ones on existing systems.
Would tea-cart sized bi-propellant rockets with electro-thermally preheated/disassociated propellants be useful?
If 64% of the energy is from existing chemical reactions then only 36% needs come from the sun. We still get roughly a 25% improvement in ISP.
ISP ~= root of energy =root of 64 = 8,
ISP ~= root of energy =root of 64+36 =10
-
#270
by
Patchouli
on 05 Jul, 2015 17:43
-
I wonder could the performance be upgraded enough to launch a Oneweb satellite as it seems like it could be a good launcher to use for maintenance of the constellation?
-
#271
by
ArbitraryConstant
on 05 Jul, 2015 20:28
-
However, I'm not sure they (resistojets) have isp-s any better than pure chemical propulsion.
They do, that's biprop ISP from monoprop from your link. Electrics contribute significantly to the heating.
Unfortunately in that case the thrust is tiny, no good for ground launch. The power required to do that at scale would be enormous. With tiny thrusters, solar can keep up.
Look at the specs, it's like 2.5 kw per newton.
-
#272
by
ArbitraryConstant
on 05 Jul, 2015 20:29
-
I wonder could the performance be upgraded enough to launch a Oneweb satellite as it seems like it could be a good launcher to use for maintenance of the constellation?
Nope.
-
#273
by
TrevorMonty
on 05 Jul, 2015 20:34
-
I wonder could the performance be upgraded enough to launch a Oneweb satellite as it seems like it could be a good launcher to use for maintenance of the constellation?
Nope.
Virgin's LauncherOne has this job.
-
#274
by
TrevorMonty
on 05 Jul, 2015 21:49
-
Virgin's involvement with Oneweb may work in Rocketlab favour. With Launcherone busy servicing OneWeb, Virgin may not have spare Launcherones to compete with Electron.
This would leave Electron's main competition as Firefly and that is not due to start flying till 2017 and 2018 commercially ( high fly rates).
If Rocketlab can have the market to themselves for 2 years they should be able to recover their setup costs and be in position to reduce prices come 2018.
-
#275
by
QuantumG
on 05 Jul, 2015 23:24
-
If RocketLab actually starts flying customers next year it's likely to have a huge effect on the smallsat market.
Of course, that goes for any smallsat launch provider who actually starts flying soon, as they'll be the first to market.
-
#276
by
TrevorMonty
on 06 Jul, 2015 00:18
-
This LV segment is going to interesting watch. Just like their cubesat payloads I expect these LVs to evolve at quicker pace than the large GTO LVs.
-
#277
by
TrevorMonty
on 22 Jul, 2015 04:58
-
-
#278
by
CameronD
on 22 Jul, 2015 05:30
-
-
#279
by
TrevorMonty
on 22 Jul, 2015 09:57
-
The air traffic south east of Christchurch is not that busy especially compared to Florida.
According to Peter Beck it is $400 for launch license.
