The thrust is pretty easy to calculate, but it WILL have a lot lower efficiency because it has to ionize the gas (which penalizes efficiency at lower Isp). At the same power, thrust will be 5 times for one-fifth the Isp (which is proportional to Isp) at the same efficiency (which is a naive assumption).
Quote from: Robotbeat on 01/21/2011 07:02 PMThe thrust is pretty easy to calculate, but it WILL have a lot lower efficiency because it has to ionize the gas (which penalizes efficiency at lower Isp). At the same power, thrust will be 5 times for one-fifth the Isp (which is proportional to Isp) at the same efficiency (which is a naive assumption).I was under the impression that VASIMR was particular because it allowed to trade thrust for isp at a given efficiency (particularly because it already works with ionized gas). I thought the reason to test the hish isp mode was a limitation of the vacuum chamber.
But weight savings doesn't come from Isp alone. For instance, if VASIMR's thrust flexibility allowed you to save an extra stage, then this too could reduce overall vehicle weight.
Quote from: sanman on 01/25/2011 04:54 PMBut weight savings doesn't come from Isp alone. For instance, if VASIMR's thrust flexibility allowed you to save an extra stage, then this too could reduce overall vehicle weight.We are talking about 5N to 20N out of an engine of 300kg + energy source. This is only good for interplanetary drive. It's even questionable if it can cross the Allen Belt fast enough (for itself or it's payload).
Franklin Chang-Diaz creator of the project, will host a conference at the headquarters of the Italian Space Agency on April 5An opportunity to learn new technology and assess the opportunities for cooperation in the field. This is the leitmotif of the event dedicated to the project VASIMIR, an innovative space plasma propulsion concept developed by former NASA astronaut and chief of the Ad Astra Rocket Company, Franklin Chang-Diaz. The meeting will be held on April 5 at 2.30 pm at the headquarters of the Italian Space Agency Viale di Villa Grazioli.
"In solar cells, the light goes into a material, gets absorbed and creates heat. Here, we expect to have a very low heat load. Instead of the light being absorbed, energy is stored in the magnetic moment. Intense magnetization can be induced by intense light"
So could vasimr theoretically be used to accelerate to say 90% c (at 9.81 m/s^2 acceleration or less), if you had a sufficiently powerful nuclear reactor??
Why does VASIMIR have a low T/W?
>The technology of advanced high-temperature superconductors has also matured significantly in the last decade with the development of commercially available high current density BSCCO and YBCO conductors by companies such as Superpower Inc. and American Superconductor. These developments have made lightweight, high-field magnets for VASIMR® applications feasible. Moreover, miniaturized cryocooler technology, such as the Sunpower M series model, has already flown in space and are being considered by Ad Astra as part of the cryogenic system for the flight magnet. Ad Astra’s VX-200 test engine features the largest cryogen-free, high-field, low-temperature superconducting magnet in existence today. This magnet was developed to meet Ad Astra’s specifications and has operated quite successfully in the VX-200 engine since its integration in May of 2009. The company is currently designing a high-temperature flight version of this system.>
Okay let me put it this way: why is the power/weight of VASIMIR bad vs. an arcjet?
Robert Zubrin launched into a rant about VASIMR on July 11, 2011 calling it a "hoax" -http://www.marssociety.org/home/press/tms-in-the-news/thevasimrhoaxPhysOrg story from July 13, 2011 -http://www.physorg.com/news/2011-07-zubrin-vasimr-hoax.htmland Ad Astra posted this on July 15, 2011 -http://www.adastrarocket.com/VASIMR_development_AdAstra_15July2011.pdfI found several problems with Zubrin's article including his contention that high temperature superconducting magnets it would find useful do not exist. Ad Astra countered that assertion in their reply -