Questions and Answers #2.pdf

Questions and Answers on RFP 80GSFC20R0028;

High Gain Antenna Flight Units for the WFIRST Project

Section 2.1 HGA Description

Context: Spec description says alignment is going to be a significant challenge.

Question #1: Can customer clarify the expectation of verifying alignment? We are assuming alignment can be verified by measuring S/Ka aperture profile and displacement maps of the reflectors, with emphasis that we are not verifying by RF testing.

Answer #1: Our expectation is to meet the mechanical alignment specification given in

3.1.3.2 of the Specification. The method of verification should be proposed by the vendor.

Context: Description indicates that FSS will be embedded on concave side. Section

3.1.2.2 (Figure 3-4) shows FSS on convex side and text says Kapton surface remain exposed.

Question #2: Need clarification on where the FSS is placed and whether it’ll be embedded or on an outer surface without additional over coating.

Answer #2: There is an error in the section 2.1. The sentence “This concave surface consists of a dielectric layer with the FSS embedded on the concave side.” should be replaced by “The FSS subassembly consists of a dielectric layer with the FSS embedded on the convex side”.

The final sentence in 3.1.2.2 is correct. The Kapton surface is outermost convex surface, thus protecting the metalized rings. There is no additional overcoating, unless proposed by the vendor.

3.1.2.1 Primary HGA Reflector

Context: Spec says primary reflector as viewed from front shall accommodate installation and removal

Question #3: What is the orientation of the reflector when installed and lifted away?

Answer #3: We don’t understand the concern, but our plan is to remove the antenna when the boresight of the antenna is anywhere from oriented down (aligned with gravity vector) to up to 90 degrees from the gravity vector.

Context: 0.1 reflection loss specified

Question #4: Spec wording seems to imply coupon testing of flat reflector material. Can customer confirm this is the expectation?

Answer #4: Verification of the 0.1 dB reflection loss can be made by historical data, measurement, or coupon test (at the discretion of the vendor).

3.1.2.2 Embedded FSS Surface Material

Context: Detailed stack up defined for FSS surface

Question #5: What is the expectation for verifying FSS surface workmanship?

Answer #5: Workmanship requirements are in Section 9 of the WFIRST Mission

Assurance Requirements (referenced in the SOW).

3.1.2.3 Ka-Band Feed Horn Subassembly

Context: There is a “shall”: … [Ka-band horn shall be positioned] such that all performance requirements shall be satisfied over all conditions.”

Question #6: This implies we are responsible for final Ka-band antenna performance requirements. Can customer clarify?

Answer #6: The vendor is not responsible for the antenna’s RF performance requirements. The vendor is responsible for mounting and aligning the GFE feed horn in accordance with the Specification.

Question #7: What adjustability is required for the horn?

Answer #7: The need for adjustability is to be determined by vendor, such that the final product meets the requirements.

Question #8: Is the customer expecting that Provider mount and align the feed?

Answer #8: Yes, the customer is expecting that the Provider mount and align the Ka-band feed assembly.

3.2.1.4 S-band Feed Subassembly

Context: Same context as Ka-band feed horn.

Question #9: Same questions.

Answer #9: Yes, the customer is expecting that the Provider mount and align the S-band feed assembly.

3.1.2.5 S-band Cable

Context: Cable routing

Question #10: Is the coax cable going to be protected with MLI? If so, who will be designing it? There may be some thermal, MMOD, etc. requirement that we do not have visibility to. If not, we will need MLI interfaces. Is it the customer’s expectation to provide in the future? This implies a cut out for the cable to go through the reflector. Is this the case?

Answer #10: We anticipate the need for some kind of thermal blanketing, such as GBK, of the cable. Yes, a cutout adjacent to the strut carrying the cable is expected.

3.1.2.6 Support Struts

Context: Support struts are required to be wedge shaped.

Question #11: Will customer be providing final profile?

Answer #11: The design of the strut cross section is to be determined by the vendor. The intention of “wedge-shaped” is that we do not want a blunt surface facing the primary reflector.

Context: Feed mass defined (.25 kg) with hat (1 kg)

Question #12: Can customer provide locations of CG relative to the mounting surface?

Answer #12: All feed assemblies have the CGs on the drawings. For the hat, assume that the CG is in the center.

3.1.2.7 Mounting Plate

Context: Spec suggests aluminum plate is a baseline.

Question #13: Will pointing requirement be relative to the reflector-side of the base plate? (i.e. aluminum plate distortions not included). If plate is included, plate may need to be Ti. Is this the customer’s expectation?

Answer #13: Yes, the pointing requirement is relative to the reflector-side of the base plate. Titanium is an acceptable deviation to be considered as part of the thermal isolation system, as specified in 3.1.2.7.

Context:

Mounting plate needs to support feed horn

Mounting plate needs to provide access to feed horn flange

Mounting plate needs to provide thermal isolation between horn and reflectors and horn and plate.

Question #14: Assume mounting plate needing to support feed horn means “needs to support feed horn support structure.” Is support required on both ends of the horn? This will induce loads onto the horn/polarizer, it is likely not the case, but it will be good for customer to clarify or provide conceptual sketch. Clarification on accessibility would also be needed since mounting plate mounts directly to gimbal, but the Wave Guide is thru the center of this plate.

Answer #14: As shown in the referenced STEP file (WFIRST-COMM-ANYS-0153), the

Ka-band feed flange is above the mounting surface interface plane. The vendor shall propose a support structure for the Ka-band feed assembly.

Context: Removal of HGA from front side while feed support structure (can) stay in place to reduce waveguide disconnections. Fasteners should also be aligned in the

“shadow” of FSS support struts.

Question #15: Does this imply support strut attachment locations can have less stringent

RMS requirement? Assume these interfaces will be bonded interface with no fasteners?

Answer #15: Exact locations of the strut attachments are not specified, provided they meet the stay-out regions defined in the STEP file. The attachment methods are to be determined by the vendor, which may be influenced by the vendor’s alignment strategy.

Context: Access to side port of polarizer needed on radiating side for GSE

Question #16: Does feed support need to be “closed off” for operation as shown in pictures? If so, what fastening schemes are allowed at this access port? Assuming a skeletal feed support is not allowed since it exposes the radiating side to metallic feed and polarizer (and hardware). If this is the case this interface will need to be replaceable. Can metallic screws be at this location? Does support need a permanent access port with no attachments?

Answer #16: The feed support does not need to be closed off, as access to the side of the polarizer will be needed. All metallic surfaces of the feed assembly can be exposed, thus a skeletal feed support could be proposed provided it provides access to the polarizer per the Specification.

3.1.3.2 Alignment requirements

Context: As-built ground vs on-orbit antenna pointing error

Question #17: Same question as above. Is it the expectation of the customer for verification of the as-built be performed with measurement of the structure? Can customer provide beam deviation factors for FSS and reflector misalignment impacts to pointing?

Answer #17: The vendor shall propose verification measurements of all surfaces for the as-built unit, and simulate and/or test on-orbit deformations as required by the

Specification.

Context: Alignment error along the Z axis

Question #18: Can this error be divided arbitrarily per Provider desire between the primary and secondary?

Answer #18: Yes, alignment error along the Z-axis can be divided arbitrarily per

Provider desire between the primary and secondary.

3.1.3.3 On Orbit Deformations

Context: Alignment error along the Z axis

Question #19: Can this error be divided arbitrarily per Provider desire between the primary and secondary?

Answer #19: Yes, alignment error along the Z-axis can be divided arbitrarily per

Provider desire between the primary and secondary.

3.2.1 Mass

Context: Whole antenna mass allocation is provided as one number

Question #20: Can the customer provide mass and cg of all GFE so contractor provided hardware’s weight allocation can be assessed?

Answer #20: The mass includes all GFE feed assemblies. Mass of assemblies are in the drawings.

Context: HGA CG limitations

Question #21: Does this include CFE hardware?

Answer #21: Yes, this includes all hardware.

3.4 Electrical grounding

Context: No ESD requirements are provided.

Question #22: Does FSS/sub reflector need to have a specific surface/bulk resistivities defined? What is the part to part resistance requirement? What is the grounding requirement for dielectrics?

Answer #22: Section 6.2.2 defines the Surface Resistivity requirement. An exception may provide for the GFE FSS Kapton surface, which is the responsibility of the

Government.

4.4 Mounting

4.5 Fields of view

Context: Requirements provided as referenced requirements to documents and models not provided/created yet.

Question #23: Can customer provide ballpark of mounting requirements and provide models?

Answer #23: Mounting requirements and models are included as part of the reference documents.

4.6.3 Alignment Stability

Context: Spec requires all interfaces to be bonded to ensure stability.

Question #24: Reflectors are mechanically attached (and isolated) from ka-band feed to allow removal and thermal isolation. Is this variation accounted for in on-orbit alignment requirements? Reflector may need shear pins for reinstallation. What is this repeatability requirement? Is repeatability all rolled into alignment requirements defined in 3.1.3.2?

Answer #24: If the vendor’s design is to not remove the feed assembly with the reflector, it is up to the vendor to propose how the alignment will be maintained.

5.3.2 Random Vibration

Context: Random vibration environment tables

Question #25: Is notching allowed per NASA-STD-7004C?

Answer #25: Notching is allowed, as described in 10.5.7 of the Specification.

5.4 Shock

Context: HGA required to survive shock environment defined.

Question #26: Since entire “HGA” is specified, does the GFE have shock requirements that will require attenuation by structure? Can all GFE be considered shock insensitive?

Answer #26: Please assume the GFE parts can survive the shock levels in the

Specification without attenuation by the structure.

7.8.4 Lift point capability

7.8.5 Lift point locations

Context: HGA requirements for lifting (20 kg with factors, etc) at specific locations

Question #27: Can customer clarify what orientation is the lift? Assume cup up with lift points evenly distributed around perimeter?

Answer #27: The assumption of “cup up with lift points evenly distributed around the perimeter” is reasonable.

8.1 Factors of Safety

Context: Table 8-1

Question #28: What factors of safety need to be applied for the thermal survival / operational requirements?

Answer #28: There are no factors of safety defined for thermal requirements. The unit shall be tested to protoflight and survival levels defined in table 5-10.

10.5 Required Tests

10.5.1 Performance Tests

Context: RF tests specified

Question #29: Is expectation of contractor to perform these tests? Can customer provide testing facilities if needed?

Answer #29: It is a requirement for RF tests to be performed pre- and post-environmental testing. The vendor may propose to delegate RF testing responsibilities and utilization of Government facilities as part of their proposal.