v3.24.4
Summary of Significant Accounting Policies - Narrative (Q3) (Details)
 3 Months Ended 9 Months Ended 12 Months Ended
Aug. 12, 2021
USD ($)
Sep. 30, 2024
USD ($)
$ / shares
shares
Sep. 30, 2023
USD ($)
Mar. 31, 2023
USD ($)
Sep. 30, 2024
USD ($)
segment
$ / shares
shares
Sep. 30, 2023
USD ($)
Dec. 31, 2023
USD ($)
segment
$ / shares
shares
Dec. 31, 2022
USD ($)
Mar. 04, 2024
Jan. 12, 2024
$ / shares
Nov. 09, 2023
$ / shares
Nov. 08, 2023
shares
Cash and Cash Equivalents [Line Items]                        
Restricted cash, non-current   $ 500,000     $ 500,000   $ 373,000 $ 312,000        
Deferred fulfillment and prepaid launch costs   1,000,000     1,000,000   1,700,000 7,400,000        
Contract with customer, cumulative catch-up to revenue   100,000 $ 0   1,800,000   300,000 0        
Contract with customer, liability   1,600,000     1,600,000   1,000,000 2,700,000        
Contract liabilities, non-current   1,143,000     1,143,000   998,000 1,026,000        
Service revenue   $ 107,000 $ 339,000   $ 1,829,000 $ 2,066,000 3,089,000 299,000        
Contract with customer, liability             $ 35,000 1,800,000        
Warrants and rights outstanding, term (in years)   5 years     5 years   5 years   5 years 5 years    
Payment of liability       $ 10,000,000                
Number of warrants outstanding (in shares) | shares                       1,716,000
Exercise price (in dollars per share) | $ / shares                   $ 0.96 $ 2  
Issuance of pre-funded warrants and warrants in private placement, net of issuance costs   $ 2,443,000                    
Estimated fair value of warrants   $ 3,000     $ 3,000   $ 3,000 564,000        
Impairments of long-lived assets         0 $ 0 0 0        
Defined contribution plan, cost         $ 0   $ 0 0        
Number of reportable segments | segment         1   1          
Number of operating segments | segment             1          
Revenue from Contract with Customer Benchmark | Geographic Concentration Risk | Geographic Distribution, Domestic                        
Cash and Cash Equivalents [Line Items]                        
Percentage of derived from customers         98.10%              
Revenue from Contract with Customer Benchmark | Geographic Concentration Risk | Geographic Distribution, Foreign                        
Cash and Cash Equivalents [Line Items]                        
Percentage of derived from customers         1.90%   39.00%          
Restricted Stock Units                        
Cash and Cash Equivalents [Line Items]                        
Expected term         6 months   6 months          
ESPP                        
Cash and Cash Equivalents [Line Items]                        
Offering period         6 months   6 months          
Common Class A                        
Cash and Cash Equivalents [Line Items]                        
Exchange ratio   1     1   1          
Exercise price (in dollars per share) | $ / shares   $ 575     $ 575   $ 575          
Expiration period         5 years   5 years          
Private Placement Warrant                        
Cash and Cash Equivalents [Line Items]                        
Number of warrants outstanding (in shares) | shares   225,450     225,450   225,450          
Estimated fair value of warrants $ 31,200,000                      
Public Warrant                        
Cash and Cash Equivalents [Line Items]                        
Number of warrants outstanding (in shares) | shares   172,500     172,500   172,500          
Issuance of pre-funded warrants and warrants in private placement, net of issuance costs $ 20,200,000                      
Patents                        
Cash and Cash Equivalents [Line Items]                        
Intangible asset useful life   10 years     10 years   10 years          
Prepaid Expenses and Other Current Assets                        
Cash and Cash Equivalents [Line Items]                        
Deferred fulfillment and prepaid launch costs   $ 0     $ 0   $ 1,300,000 3,000,000        
Other Noncurrent Assets                        
Cash and Cash Equivalents [Line Items]                        
Deferred fulfillment and prepaid launch costs   1,000,000     1,000,000   400,000 $ 4,400,000        
Cash Designated for Collateral                        
Cash and Cash Equivalents [Line Items]                        
Restricted cash, non-current   $ 500,000     $ 500,000   $ 400,000