# "rv\_to\_tle" function in satellite toolbox
**URL:** https://discourse.julialang.org/t/rv-to-tle-function-in-satellite-toolbox/69919
**Category:** Astro/Space
**Tags:** question
**Created:** [October 17, 2021, 12:57am UTC](https://discourse.julialang.org/t/rv-to-tle-function-in-satellite-toolbox/69919 "2021-10-17T00:57:21Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@sxd190026](https://discourse.julialang.org/u/sxd190026)
#### Post date: [October 17, 2021, 12:57am UTC](https://discourse.julialang.org/t/rv-to-tle-function-in-satellite-toolbox/69919/1 "2021-10-17T00:57:21Z")
I am using SGP4 package in satellite toolbox. But I want to modify bstar term at every orbit. For this purpose, I am trying to propagate a given tle for a single orbit and define a new tle at that point. Then I want to propagate the new tle for the next orbit and create another tle after that. but I am having problem with rv\_to\_tle function; it requires a matrix W which defines weights for least square algorithm. I cant define this matrix. Can somebody help me? (It says `W = I` but I dont know how to define ‘I’)
I am using python in jupyter lab and using julia through a julia interpreter called “pyjulia”
---
### Author:  [@goerch](https://discourse.julialang.org/u/goerch)
#### Post date: [October 17, 2021, 3:34pm UTC](https://discourse.julialang.org/t/rv-to-tle-function-in-satellite-toolbox/69919/2 "2021-10-17T15:34:24Z")
Isn’t this usual notation for the identity matrix?
```julia
using LinearAlgebra
I
```
prints
```julia
UniformScaling{Bool}
true*I
```
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### Author:  [@sxd190026](https://discourse.julialang.org/u/sxd190026)
#### Post date: [October 18, 2021, 3:19am UTC](https://discourse.julialang.org/t/rv-to-tle-function-in-satellite-toolbox/69919/3 "2021-10-18T03:19:17Z")
Thanks! It is.