OM-WI-02_-_VID_Strat_Alt_Prop_2017.doc

VIPER Interface Document Attachment:

Figure 1: Strategic Altitude and Propellant Report

May 2017

NASA/OP

NASA - Booz Allen Hamilton org signature

DATE

RSC-E

Rocket Space Corporation - Energia org

SIGNATURE

DATE

RSC-E

Rocket Space Corporation - Energia

ORG

SIGNATURE

DATE

Preface

This report is intended to document the results of the strategic altitude and propellant analysis performed in accordance with section 5.0 of the VIPER Interface Control Document Volume 1: Altitude and Propellant Planning. The results will be considered as the official source for strategic reboost and propellant requirements.

Assumptions

Solar Cycle Status

Altitude Strategy

Results of Analysis

84.1 US Data

244.2 RS Data

294.3 Attitude Control Propellant Assumptions

294.4 Summary of Results 2017-2024

314.5 Propellant Balance

Conclusion

1 Assumptions

· Visiting Vehicle traffic based on ISS Flight Plan CR: 15459 document, updated with changes being worked by the Flight Planning Integration Panel (FPIP)

· Russian Planning Solar Flux Forecast

· March 2009 - start Solar Cycle 24;

· September 2019 - start Solar Cycle 25;

· The profile for Solar Cycle 25 is a repeat of the Solar Cycle 24 values

· Marshall 50th percentile Solar Flux predictions for tactical time frame (through September 2018), then the Marshall 75th percentile was used through December 2019, then the Mean Russian Solar Flux predictions will be used from 2020 through Solar Cycle #25

· Marshall 50th and 75th solar cycle data from the March 2017 predictions

· Solar Arrays

· SSARJ and PSARJ are both auto-tracking

· 40° Max Off-point of the BGAs for Drag Reduction, Longeron Shadowing at high betas accounted for

· TOPO Ballistic Number (BN) and Mass Properties (Rev AG.8)

· TOPO RefTraj data continues until 2/13/2019

· Constant average ISS mass of 430,000 kg and constant Ballistic Number 133.935 assumed after RefTraj data ends in 2019

· DC1 Nadir Progress for Enhanced Roll Control (affects propellant usage)

· Russian model assumed no MLM until early 2019 to be conservative and protect for delays

· Progress propellant deliveries were modeled as:

Deliv/Progress

(kg) Annual Total

(kg) Deliv/Progress

(kg) Annual Total

(kg)

· General Altitude Strategy

· The ISS will remain at an altitude of 400 km +/- 5 km through 2019.

· Beginning in January of 2020, the ISS will climb throughout the year to reach 410 – 415 km, where it will remain through the end of the analysis. The detailed results are shown in Tables 2, 3, 4, and 5. The total propellant summary for this strategy is shown in Table 8.

· An alternative strategy was analyzed where the climb was to 415-420 km in 2020 through the end of anlaysis, in hopes of conserving propellant. The summary for this strategy is shown in Table 9.

· Visiting Vehicle Traffic Assumptions for Attitude Control Propellant Consumption Table 1: Visiting Vehicle Traffic Assumptions Through 2024 Visiting Vehicle Traffic Assumptions for Attitude Control Propellant Requirements

RS Model - 4

RS Model - 4

RS Model - 4

RS Model - 4

RS Model - 4

Note: These flight assumptions are based on FPIP, not latest Flight Schedule.

2 Solar Cycle Status

Figure 2: March 2017 Solar Cycle #24 & 25 Predictions

3 Altitude Strategy Figure 3: Assumed ISS Altitude Profile as of March 2017

4 Results of Analysis

4.1 US Data

Table 2: US Data Through 2024

Table 3: US Annual Sums Through 2024

4.2 RS Data

Table 4: RS Data Through 2018

Table 5: RS Data of ISS maneuvers Through 2024 (M=430000kg; Sbal=0,037 m3/c2 kg)

4.3 Attitude Control Propellant Assumptions

Table 6: US Attitude Control Assumptions

US ISS Attitude Control Estimates

Note1: The above data includes US assumptions for total attitude control propellant costs per visiting vehicle event.

Note2: The US attitude control values for Nadir Progress events and some Soyuz events are from statistical data (include the assumption that OPMs will be used). Therefore, these values may vary significantly from the RS values.

Table 7: RS Attitude Control Assumptions RS ISS Attitude Control Estimates without MLM

RS ISS Attitude Control Estimates After MLM

Note1: The above data includes RS assumptions for total attitude control propellant costs per visiting vehicle event.

Note2: RSC-E is assuming values produced from their ISS models (RS ADCO) as well as average statistical values.

Note 3: RSC-E values include the costs of experiments, tests, and EVA.

Note 4: RSC-E also provides values for after arrival of MLM.

4.4 Summary of Results 2017-2024

For US data, 5% was added to reboost propellant values to account for reboost attitude control and to add conservatism for unaccounted for events in the NASA software. Historic off nominal values have been up to 15% higher than predictions. Attitude control data assumed no MLM. Differences in attitude control are mostly accounted for in the RS inclusion of events such as thruster tests and experiments.

Table 8: Propellant Requirements for 410-415 km Altitude Strategy Beginning 2020

Total Propellant Requirements Summary 2017 – 2024 (410 – 415 km)

(kg)

(kg)

Table 9: Propellant Requirements for 415-420 km Altitude Strategy Beginning 2020 Total Propellant Requirements Summary 2017 – 2024 (410 – 415 km)

(kg)

4.5 Propellant Balance

Figure 4: NASA Predictions

Figure 5: RSA Annual Inventory, Delivery, and Consumption Forecast

5 Conclusion

The strategic altitude and propellant analysis shows agreement between NASA VIPER and RS data. Two altitude strategies were assessed. One assumed altitudes between 410 km and 415 km starting in 2020 for Solar Cycle #25 and the second assumed 415 km to 420 km. There is no significant benefit to either strategy regarding reboost propellant requirements through 2024. The higher altitude strategy reduced propellant requirements by 900 kg over 4 years. However, there would be a high probability of Soyuz flight aborts in off nominal situations if the higher strategy is followed.

The differences in the yearly reboost values can be accounted for by examining the method of using the monthly predictions of solar flux unit (SFU) values. A second source of discrepancies is that the RS software models elliptical orbits, while the NASA software is assuming a circularized ISS orbit. The main difference in VIPER and RS attitude control predictions was that the RS analysis included propellant for propulsive events such as thruster tests and other experiments that were not included in the VIPER analysis. The VIPER data also uses statistical data for predicting propellant consumption for visiting vehicle events, whereas, the RS analysis assumes both modeled results and statistical data.

The US modeled as 3 Progress per year through 2024, along with a conservative delivery estimate that is lower than currently anticipated by Russian manifest teams, and consequently shows a decrease below the desired levels for ISS contingency de-orbit reserve beginning in 2022 as a result of the increased solar activity peak for Solar Cycle 25. The Russian model included an increase to 4 Progress resupply flights per year beginning in 2020, along with the anticipated higher delivery numbers. These values show sufficient inventory maintained through 2024, highlighting the importance of increasing Progress frequency to 4 vehicles per year to maintain propellant inventory should Solar Cycle 25 activity align with the average level defined by the RSA model. The next analysis will be completed in 2018 for the next TIM.

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