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#1240 by speedevil on 27 Jan, 2018 16:13
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I would be astonished if this worked at 300 sec ISP. It is a monopropellant. I would expect low 200s.
The GPIM monoprop at 25N got 250, https://www.nasa.gov/sites/default/files/files/GreenPropellantInfusionMissionProject_v2.pdf
http://forum.nasaspaceflight.com/index.php?topic=35300.msg1776181#msg1776181 upthread gives another similar propellant 255 at 22N.
At 250N, the second gives 285s.
Low 200s may be overly pessimistic.
300s - probably not. -
#1241 by Lar on 27 Jan, 2018 17:15
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Mods: Is it time to create a Rocketlab directory/section? I'm seeing multiple threads here about Rocketlab, Electron, Electron launches.
It's being considered. This is a good problem to have.... but as companies proliferate there is also the danger of having so many sections that it is hard to navigate...
Rocketlab says it is moving into operational posture. That's another reason. Presumably, they will have a lot of launches in coming months. -
#1242 by TrevorMonty on 27 Jan, 2018 17:16
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Want is DV between 300x500km and 500x500km?
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#1243 by IanThePineapple on 27 Jan, 2018 17:51
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Mods: Is it time to create a Rocketlab directory/section? I'm seeing multiple threads here about Rocketlab, Electron, Electron launches.
It's being considered. This is a good problem to have.... but as companies proliferate there is also the danger of having so many sections that it is hard to navigate...
Rocketlab says it is moving into operational posture. That's another reason. Presumably, they will have a lot of launches in coming months.
I think having a "Smallsat launcher" section would be good, it can have Rocket Lab, Vector, and Virgin categories, perhaps each company can get a "General" and "Live missions" subcategory in the smallsat section too. -
#1244 by Ictogan on 27 Jan, 2018 18:01
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Want is DV between 300x500km and 500x500km?
Roughly 55m/s by my calculations. -
#1245 by Craftyatom on 27 Jan, 2018 18:18
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Want is DV between 300x500km and 500x500km?
56.452 m/s.
For a circular 500x500km orbit, orbital speed is sqrt(GM/R), where M is earth's mass in kg, R is earth's radius plus orbital altitude in meters, and G is the gravitational constant. Plugging those numbers in gives us a speed of 7616.328 m/s. That is our target speed.
For an elliptical 300x500km orbit, the easiest way to find speed at a given altitude is the vis-viva equation, which says orbital speed is sqrt(GM*(2/R-1/a)), where a is the semi-major axis of the orbit in meters. The semi-major axis is just the average of apogee and perigee (including earth's radius), which in this case is 6771km. Plugging all the numbers in (using our radius at apogee) gives a speed at apogee of 7559.876 m/s.
To find the required dV, we subtract our initial velocity from our final velocity (since both occur in the same place in space). 7616.328-7559.876=56.452 m/s of dV required.
Plugging this back into the rocket equation, we can tell what the minimum fuel mass fraction could be. If Curie has an Isp of 300, minimum fuel mass fraction is just under 2%. For a pessimistic Isp of 200, minimum fuel mass fraction is just under 3%. Of course, this is assuming the kick stage expended all of its fuel for this circularization maneuver, which it almost certainly didn't - hence "minimum" fuel mass fraction. Still, it shows why those tanks can be so dang small, especially if the density of the propellant is quite high. -
#1246 by toren on 27 Jan, 2018 19:38
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Mods: Is it time to create a Rocketlab directory/section? I'm seeing multiple threads here about Rocketlab, Electron, Electron launches.
It's being considered. This is a good problem to have.... but as companies proliferate there is also the danger of having so many sections that it is hard to navigate...
Rocketlab says it is moving into operational posture. That's another reason. Presumably, they will have a lot of launches in coming months.
I think having a "Smallsat launcher" section would be good, it can have Rocket Lab, Vector, and Virgin categories, perhaps each company can get a "General" and "Live missions" subcategory in the smallsat section too.
Perhaps move companies to a new section when they actually start commercial launches? Leave the wannabes and test phase companies here? -
#1247 by Katana on 27 Jan, 2018 20:47
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White structure instead of black CFRP? Painted white?I was actually thinking of creating a thread on the kick stage but thought it would be excessive.
I think the kick stage is a very interesting development. It raises all kinds of questions about the performance of the electric cycle and the core capability of Electron's first two stages.
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#1248 by imprezive on 27 Jan, 2018 20:48
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Mods: Is it time to create a Rocketlab directory/section? I'm seeing multiple threads here about Rocketlab, Electron, Electron launches.
It's being considered. This is a good problem to have.... but as companies proliferate there is also the danger of having so many sections that it is hard to navigate...
Rocketlab says it is moving into operational posture. That's another reason. Presumably, they will have a lot of launches in coming months.
I think having a "Smallsat launcher" section would be good, it can have Rocket Lab, Vector, and Virgin categories, perhaps each company can get a "General" and "Live missions" subcategory in the smallsat section too.
I agree. Something dedicated to the category would be nice. Maybe a small sat manufacturer subsection too? -
#1249 by IanThePineapple on 27 Jan, 2018 21:14
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I just noticed, there's a LOT of empty space at the bottom of the Curie stage. Could they add more tanks, and perhaps, more engines? Maybe even use it for the inital push to orbit (Like the Satrurn V's 3-stage design) for very heavy payloads?
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#1250 by Katana on 27 Jan, 2018 22:13
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I just noticed, there's a LOT of empty space at the bottom of the Curie stage. Could they add more tanks, and perhaps, more engines? Maybe even use it for the inital push to orbit (Like the Satrurn V's 3-stage design) for very heavy payloads?
VEB (Vehicle Equipment Bay) modified to a bonus stage? Interesting.
Possible more/bigger tanks for translunar injection of lunar X prize mission? Or this is too risky on development schedule / reliability? -
#1251 by ArbitraryConstant on 28 Jan, 2018 01:07
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Rocket Lab posted a YouTube video claiming 300 sec vac ISP in the description.This stuff seems to capable of an Isp at 300secs, be a mono-propellant and have unusually mass properties, more like a solid
I would be astonished if this worked at 300 sec ISP. It is a monopropellant. I would expect low 200s.
Solids are also monopropellants and they are capable of 300 secs vac ISP at the high end. VLM seems to have a chemistry similar to solids from the patent. So it's not obviously out of the question.
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#1252 by ArbitraryConstant on 28 Jan, 2018 01:22
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Possible more/bigger tanks for translunar injection of lunar X prize mission? Or this is too risky on development schedule / reliability?
Well the clock ran out on the lunar X Prize, but apart from that little wrinkle I think VLM would work well for a whole range of small scale BEO architectures, including lander and return stage. The thrust likely wouldn't be enough for a lander with the kick stage as built but Rocket Lab demoed VLM in a rocket fired on Earth so the thrust is clearly scalable. -
#1253 by TrevorMonty on 28 Jan, 2018 08:13
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Thanks. While 55m/s isn't lot, but it is for cubesat with little or no propulsion.Want is DV between 300x500km and 500x500km?
Roughly 55m/s by my calculations.
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#1254 by ArbitraryConstant on 28 Jan, 2018 16:28
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That makes sense, but 300s with a nozzle extension doesn't mean low 200s without.
A few solid motors get to 300 sec, but they have very large nozzles, very big expansion ratios. I don't see that with the thruster nozzle in the photo.
Rocket Lab posted a YouTube video claiming 300 sec vac ISP in the description.This stuff seems to capable of an Isp at 300secs, be a mono-propellant and have unusually mass properties, more like a solid
I would be astonished if this worked at 300 sec ISP. It is a monopropellant. I would expect low 200s.
Solids are also monopropellants and they are capable of 300 secs vac ISP at the high end. VLM seems to have a chemistry similar to solids from the patent. So it's not obviously out of the question.
We can also imagine it's somewhat formulation dependent, and perhaps some of the carrier liquids are less energetic at higher ratios. If they need lower viscosity for a small kick stage that might knock off a few more seconds. Still seems like it's in the high 200s. -
#1255 by ArbitraryConstant on 28 Jan, 2018 17:51
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Note also that hydrazine and hydrogen peroxide with catalysts don't need a spark igniter, which the Rocket Lab stuff required. Self ignition is much more fool proof for this restartable application. Now, we know it isn't hydrazine, since it was said to be "green".
This is a good point. Another thing that recommends this take is that the external appearance of the Curie engine resembles cutaways I've seen of the catalyst bed of a hydrazine thruster.
HTP is one option, and I believe N2O has also been suggested as a monoprop.
The simplicity and restartability points are well taken. I was also thinking more along the lines of delta-v needed for geostationary orbit raising, which is much more than discussed for these LEO circularization applications, I think <100 m/s has been mentioned here.
¯\_(ツ)_/¯
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#1256 by Stan-1967 on 28 Jan, 2018 18:25
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Unless Rocket Lab has gambled with its space age goo, which I doubt for this application, it would have ISP similar to these. Even if it has the goo, it doesn't have the expansion ratio for much higher ISP.
It's not like there is much to work with to estimate the ISP. All I can see is that the nozzle diameter of the thruster could be estimated by scaling it against the size of the kick stage, which should be close, but not necessarily exactly, 1.2 meters. The thrust is 120 newtons, but the prop density, mass flow rate, throat area, & theoretical ISP all all unknown. A picture & a patent, filed expertly to be as broad as possible, is not enough information to state anything definitive. Comparing against current RCS thrusters or solid rocket motors can only ballpark an estimate.
I could be wrong!
- Ed Kyle
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#1257 by msat on 29 Jan, 2018 12:14
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N2O seems unlikely if the bottle in the picture is a pressurant.
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#1258 by msat on 29 Jan, 2018 21:10
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N2O seems unlikely if the bottle in the picture is a pressurant.
They likely have a cold-gas ACS system, which could also be used to pressurize the propellant tanks. Here's a design for an HTP system that used such a setup (Option D on Page
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https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2244&context=smallsat
- Ed Kyle
Ah, yes.. Per https://www.rocketlabusa.com/news/updates/rocket-lab-successfully-circularizes-orbit-with-new-electron-kick-stage/
"Equipped with a precision pointing cold gas reaction control system, the kick stage also has its own avionics, power and communications systems."
I agree that if it's also used a pressurant, then their "green" monoprop is either H2O2 or whatever the stuff is that they developed a while back. -
#1259 by ArbitraryConstant on 31 Jan, 2018 22:01
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Rocket Lab just tweeted this:
http://www.rocketlabusa.com/news/updates/rocket-lab-reaches-500-rutherford-engine-test-fires/
Contains a bunch of stats that I don't think had been previously disclosed.
First stage engine is 5500 lbf and 311s ISP, upper stage engine is 343s ISP (I assume this doesn't count the battery pods they jettison)
First stage engine is 35 kg, meaning T/W of 71.
.