SOW_SPASS_Cryopump_Expansion_4_3_19.pdf

STATEMENT OF WORK

Cryopump Capacity Expansion for the AFIT Space Propulsion Analysis Space Simulator

Vacuum Chamber

3 April 2019

GENERAL

The SPASS Chamber currently at the Air Force Institute of Technology (AFIT) was built by

PHPK, Inc, from Columbus OH, with a center section provided by Tenney Inc. It consists of three 1.27m long segments about 2m in diameter, made from stainless steel. The chamber is designed to achieve and maintain high vacuum levels (around 10-8-10-7 Torr) and has multiple pass through provisions for instrumentation cables, thruster control, and optical access.

A. This specification lists the minimum requirements for the cryopump capacity expansion to the SPASS chamber:

(1) A total of 2 Cryopumps shall be added.

(2) Cryopumps (2) shall be CVI Torrmaster TM500 pumps to match the four (4) pumps currently installed on the chamber. These pumps have a pumping capacity of at least

2,200 standard liters of Argon at 10-6 Torr, and fit an ANSI standard 20 inch flange.

Identical pumps will simplify support and maintenance for the future.

(3) CBST 6.0 compressors (Chiller/compressor units) shall be included to provide operational power, control and compressed helium to the Torrmaster cryopumps, and one is required for each vacuum pump (two total)

(4) To allow compressor placement on a rack near the chamber, but pump placement on the chamber, helium hose sets (2 hoses per pump, 4 total), of 40 foot length shall be included, with 90 degree elbow fittings on the compressor end to permit space saving installation.

(5) Existing Power/control panel shall be upgraded or replaced to accommodate additional cryopumps and chillers. This control panel provides switchover control between the roughing pump (separate) and the cryopumps, activating the cryopumps at a programmed crossover pressure point.

(6) Training on routine maintenance tasks for the cryopumps shall be provided.

(7) Contractor shall deliver pumps to AFIT Bldg 644 rm L120, WPAFB OH.

(8) Contractor shall provide rigger services to install the cryopumps at AFIT.

(a) For the rigger services, there is only about a foot of clearance between the cryopumps and the wall at their closest point, and the pump mounting flanges are about 45 degrees from horizontal or vertical. The other side of the chamber has a similar angle, but could have about 3-4 feet of clearance if all of the equipment racks are moved.

B. The control panel part of this acquisition is an extension to an existing control panel for the six (6) other cryopumps. The current panel does the following:

(1) Starts operations by powering the mechanical roughing pump (A Screwline

250)

(2) Responds to an analog signal from a pressure gauge/vacuum gauge (a Lesker

KJL300) to activate the cryopumps when the pressure drops to about 70 mTorr.

(3) After the cryopumps are running, it turns off the mechanical pump

(4) It monitors over-temperature sensors on the compressors and pumps to shut them off if temperatures are too high in the compressor

(5) There is some separate logic for one of the pumps that sits atop the chamber and provides a "boost" to kick things over--evacuating a small chamber quite completely before the transition to cryopumps for the rest of the system.

(6) Allows a single button to shut down the entire pump system if required

(7) A control panel extension needs to work with this system to replicate these functions for the two new cryopumps. It shall be integrated to the existing panel, OR a replacement panel constructed to control all 8 cryopumps, performing these same functions.

(8) There is a 440V rail suspended from the ceiling as a potential power source for the extension panel, it would be about 15 feet from the rail to a location the Government would want to place the panel (if it is an extension).

PERIOD OF PERFORMANCE

The cryopumps shall be delivered and installed within 9 months of contract award.

DELIVERY AND INSTALLATION

The contractor shall deliver and install all hardware at the Air Force Institute of Technology

(AFIT) at the following address:

AFIT ENY

2950 Hobson Way (Area B)

Building 644, Room L120

WPAFB OH 45433

WARRANTY

Free from defects in material and workmanship, under normal and proper use for the period of time of one year after receipt.

DELIVERY PROCEDURES COMMERCIAL VEHICLES

All vehicles larger than a large pick-up truck are required to be inspected by the Wright-

Patterson Air Force Base Commercial Vehicle Delivery Gate (CVDG) prior to entering the installation. Vehicles to be inspected include, but are not limited to, the following:

1. Step van/panel truck

2. Tractor/trailer, box and flatbed containing cargo

3. Tanker trucks

4. Box trucks

5. Tour buses

6. Garbage/recycled waste trucks

7. Concrete trucks/mixers, dump trucks

8. Cranes, recreational vehicles, petroleum tanker

This inspection will be conducted at Gate 16A located off State Route 444.

The following are exemptions to vehicles utilizing the CVDG:

1. If the vehicle has the product inside (concrete and asphalt trucks) and timely delivery is necessary due to product deterioration it does not need to enter the CVDG. To bypass the

CVDG, the contractor shall submit a list containing drivers’ names, social security numbers and the state in which the driver's license is held for those drivers who will be entering the base. This shall be accomplished 24 hours prior to requested entry time. If entry is requested on Monday, this list shall be submitted by Friday at 1630 hours. All lists shall be submitted to the

88thABW/CE Directorate contract inspector. The only gates that may be used under this exemption shall be 15A, 26A, 38A, and gate 1B. If the driver's name is not on the list, he/she will not be allowed access to the installation through these gates and the base will not assume liability for denied access.

2.If a delivery vehicle must exit, and then re-enter the base to complete its route, the vehicle shall be resealed upon exiting the base. After initially passing through the commercial vehicle delivery gate, trucks shall be resealed at Gates 15A, 38A and 22B. The resealing of the trucks will allow them to continue to any other area of the installation (Areas A, B, or Kitty Hawk) without reprocessing through the CVDG. To receive resealing assistance, the drivers shall physically stop at one of the three authorized gates and request the installation entry controller to reseal their truck and provide the next location of their delivery. The controller will reseal the truck and give the delivery driver a pre-clearance form. The driver shall present the pre-clearance form to the entry controller at the next point of installation entry. This reentry can be through any base gate.

Vehicles may be subject to an inspection at any of installation entry control points during a directed random antiterrorism measure (RAM.) Any commercial vehicle, regardless of size, can be directed to the CVDG at the discretion of the installation entry controller.

(End of Statement)

BACKGROUND

The Space Propulsion Analysis Space Simulator (SPASS) chamber is used for research, testing, and characterization work related to electrostatic space thrusters. This requires that a vacuum chamber maintain a pressure of less than about 10-5 Torr (~10-8 atmospheres) to prevent destructive short circuits in the electric fields providing the propulsive acceleration. Currently, the SPASS chamber can reach pressures around 10-7 Torr when no thrusters are running.

However, when thrusters are operating, they are flowing small quantities of gas (usually Xenon or Krypton) as the propellant that is accelerated by the electric fields. This flow of gas causes pressures to increase in the chamber. The current chamber has 6 cryogenic pumps used to remove the trace amounts of gas left in the chamber after the roughing pump gets the chamber down to about 75 x 10-3 Torr, at which point conventional pumps will not support further mass removal as the gas in the chamber has reached a density too low to allow continuum flow based pumps to work. The current chamber configuration allows for a total of 9 cryogenic pumps to be installed, and there is no available real estate to install more pumps. Unfortunately, the current 6 cryo-pump set will only support gas flow rates of about 2 mg/s while keeping chamber pressures in the 10-6 Torr range. This corresponds to about a 600W Hall Effect Thruster or a slightly more powerful Ion engine. Even this level of pressure is not exactly representative of the space environment, as an altitude of 300 km (near the low end of LEO orbits) would have a pressure around 10-8 Torr and below. Especially in making high quality measurements of the properties of the plasma plumes of Hall and Ion thrusters, this increased pressure can lead to inaccuracies in measurement and incorrect conclusions, due to the interaction of the plume with an atmosphere that is over 100 times thicker than it should be. The only way to increase the pumping rate, and either allow larger thrusters or improve the level of vacuum that can be maintained, is to add pumps to the system, and to add pumps, additional chamber segments were required. An additional segment was installed and this pump expansion would take advantage of the additional pump flanges. The increased chamber volume, all by itself, will also slow the rate of pressure increase by increasing the volume of the chamber that must be filled by the propellant gas flow.

Additionally, measurements of thruster properties can be influenced by the plume impacting on the chamber walls. The individual atoms of Xenon or Krypton exit the thruster at

18 km/s or more, and strike the other end of the chamber with considerable energy, leading to wall effects on the plasma measurements as propellant gas atoms, along with some number of atoms ablated from the wall, interact with the instrumentation and the plume, altering the measurements from what would be measured due only to the unaffected plume. Adding an additional segment also increased the distance available between the end of the chamber and the instrumentation, improving the quality of measurements by increasing chamber volume alone.

Adding the segment and pump capacity will allow steady operation of much more powerful thrusters, and operation of current thrusters at lower pressure levels, decreasing the impact of background neutral particles on the thruster operations.