<p>When I first started
watchnasatv.com's you tube channel I added all the official NASA you tube channels, as subscriptions. Then hunted around for enthusiast channels that would add to the content. I was blessed to find Dr. Ben Longmier's channel, and have enjoyed following his work ever since.</p><p> </p><p>The engines in question, are his babies. I took the opportunity to reach out to him, and get some answers to your questions. I was not at all sure he would respond, he is a busy guy. Pilot, scuba diver, Post Doc rocket scientist, and one day maybe, astronaut.</p><p>Well he did, and here it is:</p><p><br /><br /> <img src="http://sitelife.space.com/ver1.0/Content/images/store/13/2/7d026c87-1a13-4393-b208-200532cf2e66.Medium.jpg" alt="" /><br /><br /><strong>Dr. Ben Longmier</strong> (weightless)</p><p><span><br /> "It seems that there is some confusion about VASIMR power levels and how this plays into testing on the ISS. One near-term goal of the Ad Astra Rocket Company (AARC) is to test a flight version of VASIMR on the ISS. The goal is to fly sometime ~2013 with a 200 kW rocket. The 200 kW refers to the total power level of radio waves, referred to as RF power, injected into and absorbed by the plasma. However, to complicate things, we plan to fly two 100 kW units side by side. There are smaller systems like cryocoolers and data systems that will draw a few additional kW, but the total power will still be close to 200kW. It's my understanding that when the Station is finished, its solar panels will be able to produce ~128kW, with about 20 kW left over to run all of the science experiments on the Station. This of course means that the VASIMR flight unit, named VF-200 for VASIMR Flight 200 kW, will have to run in a non-steady-state mode. The plan is to carry our own battery pack up to the Station. We would trickle charge the battery from available Station power over the course of a day or several days and then fire VASIMR for minutes to hours, then repeat.<br /> <br /> A few updates about the VF-200.<br /> -argon propellant (produces the optimum exhaust velocity for a 200 kW VASIMR in LEO)<br /> <br /> -high temperature superconducting magnets to produce ~ 2 tesla magnetic field<br /> <br /> -there are two RF stages, 1) ionizes the argon gas into an argon plasma, 2) heats only the argon ions (not the electrons).<br /> <br /> -two 100 kW VASIMR units will be used to form the VF-200. The magnetic field of each 100 kW unit will be antiparallel, which will create a quadrapole magnetic field overall for the VF-200. This is done so that there is no net magnetic field far from the VF-200 and thus does not interact with the Earth’s magnetic field and create a torque on the ISS.<br /> <br /> -the VF-200 is designed to produce ~5 N (1.1 lbs) of thrust. At max, the ISS has about 2 N of drag force at its current orbit and less if the solar panels are edge on to the direction of travel. A side point, but the ISS can actually ‘sail’ using this effect. The drag is caused by a small but finite air pressure at its altitude (~200 miles). Typically a Russian Progress spacecraft is used to bring fresh supplies and reboost the ISS every 6 months because of this drag."</span></p><p> </p><p><strong>He indicated that if we have any more questions, he would be happy to field them. I'll give it a week or so, and if there are further questions I'll compile them and send them to him. </strong></p><p> </p><p>He also added these from students:</p><p><span>"A few common answers to questions I get from students during lab tours:<br /> -there is no top speed for VASIMR, spacecraft speed is only limited on the amount of propellant (and current demonstrated technology keeps us way under light speed)<br /> <br /> -the magnetic field confines the plasma and keeps it away from all material surfaces. A magnetic nozzle converts the ion energy into directed thrust and expels the plasma as exhaust.<br /> <br /> -even though the plasma is super hot, it doesn’t have a lot of heat content. This is due to the fact that the plasma has a very low density (one millionth of an atmosphere for VASMIR). i.e. there is no way for VASIMR to blowup should some system fail.<br /> <br /> -a fuel tank of argon used on the ISS will last VF-200 for many years. (probably 6-12 months continues operation at full power...the tank size and launch masses are still being decided)<br /> <br /> -our goal is an overall system efficiency of greater than 60%. This means that of the 200 kW of RF power injected into the plasma stream, />120 kW makes it out into the plasma exhaust plume. The remaining 40% would be radiated as waste UV, visible, and IR light to the rocket body and out into space."</span></p><p> <span>Hope this helps,<br /> Ben</span></p><p>
Dr. Ben Longmier's You tube channel </p><p> </p><p><strong>My thanks, and heartfelt appreciation to Dr. Longmier, who goes out of his way to reach out, and share the excitement. </strong></p><p> </p> <div class="Discussion_UserSignature"> <p> </p><p> <font color="#0000ff"> www.watchnasatv.com</font></p><p> ONE PERCENT FOR NASA! </p> </div>